This is a nice phone for the money. My opinion after comparing it to a Xiaomi mi5:

Worse camera than a mi5 (but better than a Redmi note 3)
slightly faster than a mi5 when opening apps
even though the battery is 500mah bigger I found battery life to be almost identical.
Screen is on the warm side and not quite as nice as the mi5. Perfectly fine though
zui is a lighter skin than miui, it multi tasks better, it has fewer options and unlike miui I didn't find any bugs. I tried the international, indian and Chinese rom. I found the indian rom to be the best, there's no Chinese language or bloatware and it gets more regular ota updates than the international.
I thought I wouldn't like the unusual single button layout but it works really nicely and it's quick to get used to. Apple could definitely learn from this.

My only real problem with it is finger sensitivity, even running nova launcher on the most relaxed setting the screen flicks and scrolls away very quickly, if you are used to apple style finger sensitivity you are in for a shock. You could probably get used to it but the mi5 was way better for me in this regard. This and the camera/screen swung it for me and I chose the mi5.

I loaded a custom ROM in my phone just last week and here's the steps and the pitfalls you need to avoid:

This is the guide I used: http://zukfans.eu/community/threads/zuk-z2-bootloader-unlock.62/

So grab your phone S/N, install ADB and Fastboot on your PC, and install the Google and ZUK drivers.

Things to note:
If you're on Windows 8/10, you might have issues with driver signing enforcement. Bizzarely the drivers from Lenovo for the ZUK are unsigned and Windows does not like that. So you might need to disable this function. Thankfully, it's rather painless. http://www.howtogeek.com/167723/how-to-disable-driver-signature-verification-on-64-bit-windows-8.1-so-that-you-can-install-unsigned-drivers/

Now to unlock the bootloader. You'll need to go to http://developer.zuk.com/bootloader but first you'll need to register to the site. I'm assuming that you're not in China or have a chinese SIM lying around so you'll need to register using email, which can be done here: https://passport.zuk.com/wauthen3/wauth/jsp/register.jsp?lenovoid.action=uilogin&lenovoid.realm=www.zuk.com&lenovoid.ctx=JTJGc3RvcmUlMkZ6Y29kZSUyRmluZGV4LmpodG1sJTNGbnVsbA&lenovoid.lang=null&lenovoid.uinfo=null&lenovoid.cb=http://www.zuk.com/login/logincallback.jhtml&lenovoid.vb=null&lenovoid.display=null&lenovoid.idp=null&lenovoid.source=browser:m.zuk.com?lenovoid.action=uilogin&lenovoid.realm=www.zuk.com&lenovoid.ctx=JTJGc3RvcmUlMkZ6Y29kZSUyRmluZGV4LmpodG1sJTNGbnVsbA&lenovoid.lang=null&lenovoid.uinfo=null&lenovoid.cb=http://www.zuk.com/login/logincallback.jhtml&lenovoid.vp=&lenovoid.display=null&lenovoid_idp=null&lenovoid.source=browser:m.zuk.com&lenovoid.thirdname=null&lenovoid.qrstate=null

Once you register, fill in the bootloader unlock form and you'll get an email with some Chinese writing, this is unimportant. Look at the attachment to that email and you'll find a unlock_bootloader.img file. Download it and you're in business.

Now I ran into trouble sending fastboot commands to my phone, just wouldn't be detected for some reason, no clue why. But I found this tool by mauronofrio: https://forum.xda-developers.com/zuk-z2-pro/development/tool-tool-one-driversunlocktwrpfactory-t3432782 - works like a charm, you can use it to unlock the bootloader and then install TWRP on your phone.

Once you have TWRP then you can install whatever ROM that tickles your fancy, no problem. Personally I'm running Resurrection Remix by fedor917 https://forum.xda-developers.com/zuk-z2-pro/development/6-0-1-unofficial-resurrection-remix-t3504145 I tried CM14.1 but it's not stable enough for me and I much prefer RR. Plus it's Marshmallow so xposed works fine on it and plenty other stuff that hasn't reached Nougat yet. I really want Nougat-based Resurrection Remix on this phone and I've been working at porting it, but it's the first time I do this so it's quite a steep learning curve.

To unlock bootloader
http://zukfans.eu/community/threads/zuk-z2-bootloader-unlock.62/

To get TWRP
https://twrp.me/devices/zukz2.html
Follow the Fastboot install method

To get Mokee
https://download.mokeedev.com/?device=z2
Install this via TWRP

Done.

If you like big screen phones
The best phone Now is Samsung Note 4 you can get up to £300 for new / nearly new or used less 200
This my opinion Why get cheap chines phones with no updates etc
Get 2 Years old phone with all best hardware at this time It is still going strong and will be for another couple years
Got everything what other phones now do not have

I have dropped accidentally from 2 Meter high on tiles and I have marks on frame the screen is top quality very hard to break compare to new phones likes S7 or S6 or note 5 Anyway you can buy frame for £10 and double side tape and replace the frame and will be like new again

Now do same thing with new glass phones you drop game over shattered Battery can not replace the screen curved and so easy to crack

White only at this price, black is £144 with code, but good value. Its a china only phone , and no updates.

http://www.trustedreviews.com/lenovo-zuk-z2-review

White only at this price, black is £144 with code, but good value. Its a china only phone , and no updates.

http://www.trustedreviews.com/lenovo-zuk-z2-review

Here's my post on this phone last time with some information about the phone in there:

http://www.hotukdeals.com/deals/lenovo-zuk-z2-5-0-fullhd-1080p-snapdragon-820-4gb-ram-64gb-storage-4g-lte-white-2503278

Gave it to my sister straight away however when it arrived and didn't really play with it so unfortunately I didn't really get back to the thread to post a review. I can say say that it was pretty nippy and was almost as fast as my OnePlus 3 when I ran some app tests side by side with her.

Here's my post on this phone last time with some information about the phone in there:

http://www.hotukdeals.com/deals/lenovo-zuk-z2-5-0-fullhd-1080p-snapdragon-820-4gb-ram-64gb-storage-4g-lte-white-2503278

Gave it to my sister straight away however when it arrived and didn't really play with it so unfortunately I didn't really get back to the thread to post a review. I can say say that it was pretty nippy and was almost as fast as my OnePlus 3 when I ran some app tests side by side with her.

Assuming this is the 'Pro' version it has an xda forum: https://forum.xda-developers.com/zuk-z2-pro

(and therefore plenty of dev interest, incl custom roms)

This is *not* the pro version....

Fair enough

this would be great but from what I believe you have to flash a rom to get google play store to work & it cant just be used out the box