dont worry about heating
I got a ZR over a month ago. I am very happy with it. There is no need to worry about heating issues.
I live in hyderabad where the temperature is very high (i wont say it's the highest in the world). When I play games for more than 30 minutes i had felt the device getting heated up - I just wipe it with cold water or pour a bit of cold water and it cools down - it is a waterproof phone after all.
The only drawback of the phone is the front camera (0.3 mega pixel) . But i never use video calling so that's fine with me.