I bought this phone a week ago, after a lot of research and hunting reviews for the phone (which were mostly Russian or Spanish for some reason). It was suppose to replace my dying LG G2, and it does a damn fine job at that!
The phone is well built (unlike my G2...) and feels good in the hand. Even for it's size, the device is very thin and I can almost handle it in one hand (I am of average height, 1.78m).
It's clearly made of metal (most of it at least), since I freeze my hand on it every morning. The buttom and top parts are plastic, which kind of sucks, but it's nothing I really noticed while using it. The home button isn't as "cheap" as I've heard it were either. The durability of this design is to be tested!
The 5.7' display is great too - sharp, vivid and colorful. I noticed it has a different color scheme than my G2, but it was only when I compared them side to side. To be honest, even if it's not color-accurate as my G2, I wouldn't have even noticed or cared. The resolution is very adequate for this size still, and I can barely see any pixels (and only if I look real close and squint). 1440p is not needed here!
The battery life is fantastic as well, I saw a noticeable improvement over my G2 - I used to get around 5-6 hours of video streaming on it (Youtube, Twitch) and now get around 7-8 hours on this device (with comfortable screen brightness), and for roughly the same battery size! (~3000mAh). Standby time is to be improved though - google play services seems to be draining me dry for some reason!
I had zero issues with Flyme OS - I bought the international version of the phone, and it came out of the box with ver 4.5.X, but I immediately updated it to version 5 in by far the most painless and fast method I've ever witnessed - downloaded the Flyme 5 zip for my model (from Meizu's site), copied to phone, opened file through file manage and boom - it's upgrading.
In addition the phone came with ZERO chinese bloat, so my inner geek was more than pleased to see English everywhere and a near empty app drawer in Nova launcher!
The UI itself is no where bad as I expected it to be - It's super fast, very fluid and very nice to look at. I find it very intuitive to use and it's much better than TouchWiz or LG's UI for me. I even like the stock launcher and the "Security" app which handles app permissions, choosing which apps idle and "cleaning". Heck, you can root the device FROM THE SETTINGS MENU. YES! (Locked boot-loader though...).
The fingerprint scanner seems to work perfectly fine for me, although it can be very finicky when it comes to what part of the finger you use. A good re-scan helped
Overall, I would say this phone is very good for the price I paid for it. I could have gotten a 32GB Galaxy S6 for the same price, but instead I chose the 64GB of the Pro 5, which has superior battery life, better software experience (for me), expandable storage, bigger screen and less fragile build. I highly recommend this device!
UPDATE: Software problems solved. There is an app called 'Security' (which controls everything in fact) and although I gave every permission for the apps (Google, Google Now launcher, Messenger), this app overrid them. So you just have to go in there and give the permissions you want to give and everything will work fine.
But I noticed another issue: you download something from the Google Play Store and some time after that it starts behaving in a weird way (NFS No Limits got another icon and it started downloading some 'skin', which I never heard of and it looked like some virus...). I found out, that the original App Store (every Chinese phone has an own app store) updates the apps without a warning or notification. So to solve this you have to disable auto update within the Chinese app store.
Great phone specwise, it offers everything (except OIS), what a western flagship has. The build quality is also excellent (many reviewers say, that the home button feels cheap, but I don't think so).
The only problem is the software, but nothing too bad (that you can't live with it). It's evident, that the phone is Chinese and the developers didn't calculate with customers from other countries (although, the Flyme OS offers a wide range of languages). You can run into some Chinese stuff here and there (Chinese writings, which you don't understand, and the pre-installed stuff, which only work in China), but it's not that bad, that you can't live with it. Also the phone runs great and smooth UNTIL YOU STAY WITH THE STOCK THINGS. The Flyme UI is OK, but I like the stock Android more, so I installed the Google Now launcher. It sometimes chrashes and throws me back to the stock launcher (although in the settings the Google one is set as default). But if you stick with the default launcher, it's flawless, just you don't get an app drawer... Another (a little) annoying thing is that it prevents the Facebook Messenger from accessing the net if you closed that down in the recent apps. So you won't get your messages unless you leav it running in the background (with the 4GB RAM model it's bad only for the battery). However, we must consider, that Google and Facebook is banned in China, so the devs didn't care too much optimising these apps (which is understandable from one side, but too lazy from the other).
Conclusion: It's a great phone with some (only software) comprises. But you can either live with that or root the device (which is a built in feature in the OS) and flash another ROM on it, because the hardware is excellent. And don't forget, that you get this kind of performance and quality for half the price of a western/Korean flagship.
(And it's so good to listening to music with it, even with the stock music player, thanks to the dedicated audio chip)
What I changed:
Stock keyboard to Google kb.
Flyme UI to Google Now launcher
Stock browser to Chrome
Stock cloud-service to Google Drive
(Optional: stock music player to PowerAmp)