I've had my Z5 for a few weeks now, and I'm loving it!

The battery life, compared to my Z1, and the Galaxy S5 I used for a week prior to getting this (after my £20 Vodafone phone broke), is brilliant. With heavy usage (gaming, YouTube etc), it gets me through a day. 

Overheating isn't an issue either (as the 810 chip is infamous for), unless I'm playing games, listening to music, using Snapchat and messenger at the same time (Even then it's not 'hot'). Performance is as good as you'd expect. 

One thing that surprised me was just how quick and reliable the fingerprint scanner is, it works first time, 99% of the time. 

Memory management isn't an issue either, something I found annoying on the Galaxy S5. I return to games as I left them, when I leave to send messages, whereas all to frequently on the S5 it had to reload the game. (I know the S5 is older, but it still has a cracking processor, and 2GB RAM)

Overall, if anyone is in the market for an Android device, I'd highly recommend this, especially as it's now come down in price.