ZUK Z2 Review

ZUK Z2 (Z2131) is the latest (and currently third) smartphone of the ZUK brand backed by Lenovo. The model has been originally created for the Chinese market, but the huge interest in it definitely puts a pressure on ZUK for creating and international ROM for the device. It has already been confirmed that it will be launched in India as the Z2 Plus. On paper, the model builds upon what ZUK Z1 has already provided - good design, noteworthy features and an affordable price. In the review below, we will have a deeper look into the design, specifications and performance of the device, which has its original domestic ROM version, adapted in English.

Specifications

ZUK Z2 sports a 5-inch IPS LTPS display with an FHD resolution (1080 x 1920), which results in a pixel density of 441 ppi. It is covered with a 2.5D curved glass screen and a Corning Gorilla Glass 4. It covers 70% of the NTSC color space, has a static contrast ratio of 1000:1 and a peak brightness of 400 cd/m². The model's hardware is based on a Qualcomm Snapdragon 820 MSM8996 system-on-chip. It includes 2x 2.15GHz Kryo CPU cores and 2x 1.6GHz Kryo CPU cores. They are coupled with a 624MHz Qualcomm Adreno 530 GPU, which is responsible for the graphics. The chipset also includes a built-in Hexagon 680 SPU. There are 4GB of double-channel LPDDR4 RAM clocked at 1866MHz on board along with 64GB of eMMC 5.1 internal memory (non-expandable). The smartphone packs a bunch of advanced sensors such as heart rate, UV, pressure altimeter, three-axis accelerometer, three-axis gyro, G-sensor, three-axis compass, etc. Of course there's a fingerprint sensor with the U-Touch 2.0 as well. As long as it concerns the cameras, ZUK Z2 features a 13-megapixel Samsung S5K2M8 ISOCELL sensor for the primary shooter, which is coupled with a 5-element, f/2.2 lens, PDAF + CAF dual-mode focus, single LED flash. The front-facing camera is equipped with an 8-megapixel OmniVision OV8865 sensor and a 5-element, 78.9° wide-angle lens. The lights are kept on by a high-density 650Wh/L battery with a capacity of 3500 mAh. It is combined with a 5.3V/2.5A charger and Qualcomm Quick Charge 3.0. The advanced chipset provides advanced connectivity options, which include dual-band Wi-Fi a/b/g/n/ac, 802.11n 5GHz, Wi-Fi Hotspot, Wi-Fi Display, Bluetooth 4.1. The device supports 2G GSM, 2.5G CDMA, 3G WCDMA and TD-SCDMA, 4G FDD- and TDD-LTE networks as well as GPS/A-GPS, Glonass, BeiDou, and Galileo. A USB Type-C 2.0 port along with a 3.5 mm jack are on board as well. ZUK Z2 runs Android 6.0.1. Marshmallow with ZUI 1.9 on top. For the full list of ZUK Z2 specifications you can check the model's page.

What's in the box

ZUK Z2 arrives in a rectangular white box with the ZUK by Lenovo logo on top with a photo of the product, while on the back there is information about the specifications and TENAA licensing of the unit. Inside, in the top level compartment lies the smartphone itself and below it are the two-pin wall charger (US NEMA-1 plug standard) with output power of 5.3V/2.5A and the USB Type-C cable. The charger has two flat pins, so you will need a plug adapter, if you live outside the US, Canada and some Latin American countries. Of course, there are a user manual with some other booklets and a SIM ejector pin.

Design, build and controls

ZUK Z2's design is pleasantly refreshing as it deviates from the curvier designs of most smartphones today. Its clean lines, matte frame and glass front and back create an elegant and sober appearance. Both the front and the back are covered with durable glass with oleophobic (lipophobic) coating, but it actually works only for the back. Smudges on the front are clearly visible. However, what is more important is that you have to be careful where you place the device as its glass back tends to be very slippery on hard surfaces. Holding it in the hand is very comfortable, though, and there's no risk of slipping off. The chassis is made of titanium-aluminum alloy. The White Z2 has anti-pollution coating, making it more dirt-resistant. The Black Z2 has a metal particle coating, like SLRs, making it look more substantial. We are reviewing a black unit. The tough fiber-glass frame has chamfered edges on both sides and is beautifully matte. The seams between the glass and frame on the front and back are tight and perfectly matched. With a width of 68.88 mm, the model is one of the narrowest smartphones with 5-inch displays. The only other devices that currently have a lower width are the Amigoo V10, Jinga Basco 500, Lyf Earth 2, and Sony Xperia XA. The height of the smartphone is 141.65 mm, which is very compact as well for this display-size class. With a waistline of 8.45 mm and a weight of 149 grams, ZUK Z2 is the thinnest and lightest smartphone among currently available devices with a 5-inch display and a 3500 mAh battery. You must not have doubt about it - the smartphone has an excellent build. All elements fit perfectly and the overall look and feel is of a high-end device. ZUK has opted for an unusual setup of the controls, either. The left and top frames of the device are entirely clean. The bottom one houses a 3.5 mm jack, microphone hole, a USB Type-C port, and a grille with a single speaker behind it (from the left to the right). The right frame is where you'll find (from the top to the bottom) - a single volume button, the power button and towards the lower end - the dual-SIM card tray. Bear in mind, that ZUK Z2 does not provide expandable storage, so this tray is suitable for using two nano-SIM cards only. On the rear are placed the primary camera with a flash and a microphone hole towards to the top, while towards the lower end the ZUK logo is printed. On the front, above the display are the selfie camera and the earpiece. Below the display there is a single button, which is both touch- and pressure-sensitive and performs all functions of a navigation bar. Yep, this is an unusual design feature for an Android smartphone. Understandably, iPhones are excluded. Moreover, it has an embedded fingerprint sensor. A short tap on the home button serves as a "back" command, two presses loads the list of active apps, pressing the button leads to the home screen. Swiping to the left and right navigates through the various desktops. This function does need some time to get used to, but once you do, it is as convenient as any other navigation bar.

Display

ZUK Z2 is equipped with what it calls a "Super Retina Display". This is a 5-inch screen with an LTPS IPS panel that has a resolution of 1080 x 1920 pixels and a pixel density of 441 ppi. LTPS (Low Temperature PolySilicon) panels are used in displays with large size, large resolutions and pixel densities because the electrons move faster through the polysilicon grains and the pixels can be placed close to one another. The panel of the model has a classic striped pixel structure. According to the official specifications the display has a 1000:1 static contrast ratio, 400 cd/m² brightness and covers 70% of the NTSC color gamut. The unit is protected by a Corning Gorilla Glass 4 with a 2.5D curved top glass layer. The same protects the back. Both have an anti-stain coating, but actually you can see smudges left from your fingers, more on the front than on the back. In terms of displayed content our subjective opinion is that colors are true-to-life and text rendering is excellent. According to our display measurements, our review unit has a peak brightness of 530.364 cd/sq.m. It drops more than twice to 237 cd/sq.m. when the brightness level is set at 75%. At 0% the white luminance value is very low - 3.225 cd/sq.m. At the same time the black luminance value at this level couldn't be measured, hence, the static contrast ratio is not measurable too. The black luminance values at all brightness levels decrease proportionally compared to the white ones, therefore, the static contrast ratio remains almost the same at all brightness levels (excluding 0%) - an average of 1100:1. The temperature of the white point is around 8600-8800K, which is higher than average (the colors look colder) displays in general, but for a smartphone display it is a normal level. In case you need to adjust the color temperature, you can do so from the corresponding display options from the Settings menu. Regarding the colors, the display of ZUK Z2 covers less than 100% in the red and green spectrum of sRGB, while in the blue one there is a slight deviation from the sRGB one. This entirely complies with the 70% coverage of the NTSC color space as officially specified. Horizontal and vertical viewing angles are very good with only a slight loss in brightness when the display is looked from aside.

Brightness	White luminance	Black luminance	Contrast	Color temperature
100 %	530.364 cd/m2	0.481 cd/m2	1103 : 1	8754 K
75 %	237.274 cd/m2	0.216 cd/m2	1098 : 1	8608 K
50 %	142.802 cd/m2	0.133 cd/m2	1074 : 1	8630 K
25 %	41.579 cd/m2	0.038 cd/m2	1094 : 1	8657 K
0 %	3.225 cd/m2	0.000 cd/m2	-	8841 K

OS, UI and software

ZUK Z2 runs Android 6.0.1 Marshmallow out of the box with ZUK's proprietary UI on top - ZUI 1.9. The ZUI version our review unit has is 1.9.077-ST. It is bound to be updated to the next stable ZUI version - 2.0, but since ZUK's servers are geo limited (access from China only), the update could not happen over the air. So we're currently reviewing ZUI 1.9. This is the adapted English version, but still has some apps and settings in Chinese. This user interface differs in many ways from the classic Marshmallow one and other custom UIs we've reviewed. The lock screen allows access to the camera app by swiping it to the left. Swiping up unlocks the device. Notifications and access to the Quick Settings on the lock screen are allowed by default, but you can change that from the Settings menu. The home screen has a docked row of apps, which includes the Dialer, Messenger, Browser and Camera. Above it there are two rows of on-board apps. You can swipe the screen to the right, which gives you access to the U-Health app. Swiping to the left allows you to navigate through the various desktops with apps. There's a Tools folder containing several apps inside, but the interesting thing about it is the option to rename the folder. Once you open it, you'll see a blinking cursor next to the folder's name and you can change it. There is no Widgets menu in ZUI. The only thing that is widget-like is the clock and weather app on the home screen, which you can edit. A long press on the home screen opens up an option for re-arranging the apps. Another major difference is the access to the Quick Settings. You have to swipe up from the bottom of the screen to open it. It has two screens, the second is accessed by swiping from the first screen to the left. From the Settings menu you have toggle options for the Quick Settings. The Notifications can be opened by swiping down from the top of the display. The volume screen has two options - system and media sound volume. When you press and hold the power button you get access to the reboot menu. It includes two options only - reboot and power off. A double press on the home button opens the list of active apps. If you swipe down an app, you will lock it, thus protecting it from cleaning. To unlock it - swipe down again. The Settings menu is deeply reorganized compared to a standard Marshmallow one with many options brought up a level or two above, so they are accessed more easily and quickly. It starts off with the connectivity options, which include all standard ones. More interestingly, options like Roaming services, Personal Hotspot and VPN connections are placed in a totally different section named Advanced Settings. The first menu after the connectivity one is the U-Touch, which manages the behaviour of the home button of the device. As mentioned earlier, it is both touch- and pressure-sensitive. From this menu you can adjust its behaviour as a navigation button, while its function as a fingerprint sensor is managed from the corresponding menu. The Notifications & Statusbar set of options is extensive and lets you adjust which apps should produce notifications and which not. You can also toggle on and off the badge appearance on three apps - Messenger, Dialer and System updater. This section also includes options for the Notification light, which is switched off by default. Third come the settings for the Quick menu. You can change the switching sequence and toggle the shortcuts. ZUI does not rely on colorful themes and wallpapers to attract the user. It lets you choose from several beautiful wallpapers available on the smartphone and many more, which can be downloaded for free. You can switch on a daily wallpaper function and HD desktop wallpaper. You also have four skins to choose from - the default one, black, blue and red. ZUI gives you a choice of various fonts, however, they are available only for Chinese. The Display settings allow you to switch on a Night Color mode, which warms up the display. If it is switched off, you can choose from cold, standard and warm color options. From here you can also change the text size and set a screen timeout. The Sounds & Vibrate section includes the standard Volume, Vibrate, DND, Ringtones, Sound notifications, but also a Headset buttons calibration. The Fingerprint & Passcode menu lets you set up your fingerprint ID(s), which is fairly quick and easy. You must set up a PIN, password or pattern in order to activate a fingerprint ID. However, when you delete the ID, the passcode you have chosen remains. The Security settings are not as extensive as those in the classic Android M. They include a Screen pinning option, app permissions settings and strangely - the location mode, which has more to do with connectivity and battery usage. The Advanced settings include options for the Date & Time, Language & Input, Account synchronization, Auto power on/off (Scheduled...). Under this section you can also monitor and manage the battery, storage, applications, several connectivity functions such as Personal Hotspot, Roaming and VPN, Network settings reset and a separate Factory data reset. It also contains the standard Accessibility options. The last section of settings includes the Cloud Service, for which you must have a ZUK account, the Phone/Call, Contacts, Messaging and Camera settings. At the end are the System updater and About phone details. ZUK's servers are geographically limited to be accessed from China only and an OTA update outside the country is impossible, unless you use a reliable VPN service or other tools (not OTA) to install the update. ZUI is very clean in terms of pre-installed apps. Its Chinese version is much richer, but we are reviewing the adapted English one (official). Unlike the Chinese version, this one has Play Store pre-installed along with Google Play Music and Calendar. You get all the standard apps such as Dialer, Contacts, Messenger and default Browser. The Dialer has an option to switch the its additional menu to the left or the right of the dial pad. This menu has an integrated shortcut to Yellow Pages in Chinese. The Calculator seems to be standard, but the Clock app is modified and has four different screens for the alarm, clock, stopwatch and timer. Another app that is in Chinese and needs a ZUK account is the U-health one. Of course, there is a File Manager, along with a Gallery, Camera and a Weather app. The Tools folder contains the Sound Recorder, Calculator, Compass and a shortcut to the System Updater. The compass can be calibrated and contains a level tool as well. Finally, there's an app called SafeCenter. Some of its settings are in Chinese, but the main functions are in English. The first one is the storage monitor, which can assess memory usage and suggest clean-up services, so you get the most out of your storage and accelerate the device by freeing RAM. The second screen of the app is called AntiVirus, but contains various services such as Accelerate (again by freeing RAM), Space Cleanup (by optimizing apps), Data Usage monitor, Autostart app toggles, App Permissions toggles, and Anti-Spam options.

Networks, calls and connectivity

ZUK Z2 has a dual SIM card slot for nano-SIM cards. Only the first slot supports 4G LTE Cat. 6 for up to 300 MBit/s in downstream and 50 MBit/s in upstream. The second SIM card works with 2G and 3G connections. The network bands supported by the device include 2G GSM (850, 900, 1800, 1900 MHz), 2.5G CDMA 800 MHz, 3G W-CDMA (850, 900, 1900, 2100 MHz), 3G TD-SCDMA (1880-1920, 2010-2025 MHz), 4G FDD-LTE (850, 900, 1700/2100, 1800, 1900, 2100, 2600 MHz), and 4G TDD-LTE (1900, 2300, 2500, 2600 MHz). Call quality has been excellent at all times, both for the caller and receiver. The rest of the model's connectivity options include dual-band Wi-Fi a/b/g/n/ac, 802.11n 5GHz, Wi-Fi Hotspot, Wi-Fi Display (Miracast), and Bluetooth 4.1. Wi-Fi reception has been stable and setting up the device for its various wireless connections is quick and easy. There's a USB Type-C 2.0 and NO OTG support. The model operates with the three main satellite systems - GPS, Glonass and Beidou, and has managed to detect a good number of satellites from all three with an accuracy of up to 3 meters. There are additional connectivity services such as setting up a Private Hotspot, VPN, and Roaming service, which can be accessed from the Advanced Settings. There's also a Network Settings Reset function, which is separate from the Factory data reset.

Performance

ZUK Z2's performance relies on a Qualcomm Snapdragon 820 MSM8996 chipset. It has two 2.15GHz Kryo cores and two 1.6GHz Kryo CPU cores, working in tandem with a 624MHz Qualcomm Adreno 530 GPU, which handles the graphics. The built-in Hexagon 680 SPU is used for functions, such as the pedometer, which do not require much power. It works independently from the CPU and adds to the overall power efficiency of the chipset. More interestingly, in the latest official and stable ZUI, ZUK has provided a one-click overclock mode, which boosts the clock rate of the CPU to 2.30GHz. Obviously, without being able to update to the latest UI we cannot run the benchmark tests and actually see whether this brings any significant boost in performance. Our unit scored 131789 points in AnTuTu, which means that it only slightly outperforms the nubia Z11 (131119) and ZTE Axon 7 (130536), taking up a third place in our chart of reviewed smartphones with a Snapdragon 820 SoC. The first place is occupied by OnePlus 3 (144140) and the second - by LeEco Le Max 2 (137549). However, when you look at the PCMark Work performance score, it definitely places the ZUK Z2 on top of all devices with 7278 points. The Geekbench 4 results are significantly lower to the results of the other smartphones, tested with Geekbench 3, so we cannot actually compare them fairly. The Basemark X gaming performance score of ZUK Z2 is very close to the one of OnePlus 3. The top place in this regard is taken by the nubia Z11. The system-on-chip is combined with 4GB of double-channel, LPDDR4 RAM clocked at 1866MHz. The built-in memory measures 64GB and is of the eMMC 5.1 type - the fastest eMMC one. This means that the PCMark Storage score and the results from the Androbench test are expected and are close to those of nubia Z11 and lower than those of the OnePlus 3 (the device with the fastest memory according to its scores) and the Axon 7. Of those 64GB, 58.24GB are available for the user. There is no option for memory expansion. The device also has an advanced sensor setup. It has a heart rate and UV sensor, pressure altimeter, three-axis accelerometer, three-axis gyro, G-sensor, three-axis compass, proximity and ambient light sensor, Hall sensor, pulse oximeter. Besides helping the device to provide you with immersive gameplay, they also serve ZUK's U-Health app. The multi-functional home button has an embedded fingerprint sensor (model FPC102x), which supports wet fingerprint unlocking. It is coupled with ZUK's U-touch 2.0 software, which supports HD fingerprint identification and self-learning fingerprint matching algorithm. This means 99.8% accuracy and fast recognition in 0.1s. From the corresponding section in the Settings menu, you can tweak the U-touch options and manager your fingerprint ID(s), respectively.

Cameras

The camera app is pretty simple. Its home screen has a large shutter button, merged with a smaller one on its right that serves as switch between the front and rear shooter. On the left is the shortcut to the video function and on the right - to the gallery. At the upper end of the screen you'll see the icon for the LED flash options (in the left corner) and HDR ones (in the right corner). In the center between them you have the camera modes icon. It opens a list with options, including HDR, flash, Pano, Scale as well as HFR (high frame rate) and LFR (low frame rate) options. If you've opened the selfie camera, there's a beautification function with its corresponding icon in the top left corner. There are additional camera settings, which let you choose the resolution and quality of photos and videos, manage several sound effects, and etc. Editing a photo includes applying several filters on it, changing its aspect ratio, rotating it to the left or right, and so on.

Primary camera

In order to appeal to fans of photography, ZUK Z2 has chosen a 13-megapixel Samsung S5K2M8 ISOCELL sensor with a 1/2.6" size. This sensor is seldom used in mobile devices. The only other devices that have it are the 360 Q5 and Q5 Plus. ZUK has coupled it with a 5-element lens with an f/2.2 aperture, single LED flash, and a dual-mode focus, which joins phase-detection autofocus (PDAF) with continuous autofocus (CAF). The latter is used for fast moving objects as it detects their movements and refocuses accordingly to keep them sharp. The images are with a resolution of 4160 x 3120 pixels, while the top video resolution is 4K (3840 x 2160) @ 30 fps.

Secondary camera

The front camera features an 8-megapixel, 1/3.2-inch OmniVision OV8865 sensor with a 1.4-micron OmniBSI-2 pixel and a 78.9° wide-angle lens. The sensor's model has been announced three years ago, but still it does a very good job in this smartphone. The images are with a resolution of 3264 x 2448 pixels, while the top video resolution is 1080p @ 30 fps.

Audio

ZUK Z2 shows audio results that are only very slightly better than those of an average smartphone. The test has been performed by using the the RightMark Audio Analyzer software and the TASCAM US-2x2 audio interface. The device does not have any special audio equipment and has a single speaker placed at the bottom frame next to the USB Type-C port. Yet, the sound from it is good (subjectively speaking). ZUK uses Google' music app, instead of providing one of its own, and it does not have any advanced audio settings. Under the Sound options from the Settings menu you can choose to calibrate your headset buttons.

Test	Value	RMAA rating
Frequency response (from 40 Hz to 15 kHz), dB	+0.01, -0.09	Excellent
Noise level, dB (A)	-90.5	Very good
Dynamic range, dB (A)	90.9	Very good
THD, %	0.0041	Very good
THD + Noise, dB (A)	-82.6	Good
IMD + Noise, %	0.0094	Very good
Stereo crosstalk, dB	-81.1	Very good
IMD at 10 kHz, %	0.014	Very good
General performance		Very good

Battery

ZUK Z2 is powered by a high-density 650Wh/L Li-Pol battery with a capacity of 3500 mAh. It is non-removable and has a fast charger with an output power of 5.3V/2.5A that employs a dual parallel chip for faster charging. The latter is supported by Qualcomm's Quick Charge 3.0 technology. There are several battery life optimization options scattered around the Settings menu. For example, the Battery Saving option, regarding the use of location services, is located under Security > Location. Auto Power On/Off (a.k.a. Scheduled power on & off) can be found under Advanced Settings and is separate from the Battery settings, which are part of this group of options. The latter allows you to monitor the battery percentage and choose whether it should appear next to the notification icon or not. You can also monitor the amount of power consumed by apps and hardware parts. You can choose to have a manual battery saving mode or enable it to start automatically, when the charging level reaches a pre-defined by you percentage. During our test period, the battery showed very good results in terms of stamina. It has an excellent result from the PCMark Work battery life test for a 3500 mAh accumulator - 9 hours and 14 minutes. The test has been made with the display's brightness calibrated at 200 nits, following Futuremark's recommendations for proper testing. The fast charger is a small unit with two flat pins that tends to become hot, while charging. It has an output power of 5.3V/2.5A, which is not very common. However, it performed really well during our charging test. The first 10% of charge were with a rate 1% per minute, than the rate escalated to 5% per 3-4 minutes, till the charge reached 55%. After this charging speed slightly slowed down again to 1% per minute, till the battery capacity reached 85%. The battery reached half of its capacity from 0% for 37 minutes. It needed another 35 minutes to reach 85%. After that the charging slowed down more noticeably. It needed 17 minutes to charge from 85% to 95% and the final 5% needed 28 minutes to charge. It took almost 2 hours (1 hour and 57 minutes to be precise) to charge the battery from 0% to 100%.

Final thoughts

ZUK Z2 is an excellent smartphone in its price class. Currently it can be purchased for as low as USD 260. You get a lot for your bucks, including high-end design that is unusual (compared to current trends) and will equally suit your business and private lifestyle. Masterfully crafted, the smartphone is very compact and easy to use. Along with its design, it has several other noteworthy features that make it stand out from the crowd such as the single-button U-touch navigation and ZUK's proprietary UI. In terms of hardware, the smartphone shows some real power and is able to put its high-end chipset and 4 gigs of RAM to good use. It can also serve as a connectivity hub providing various ways for wireless communication along with support for quite a bunch of network bands. The camera and audio are standard for a device of that class, and battery life is excellent. To wrap it up - ZUK Z2 is a reliable smartphone and companion in your day-to-day tasks and entertainment with an excellent feature/price ratio and if this is important to some of you - you won't pass by unnoticed when using it.