I've used the S3 Mini and HTC Sense which I know is ancient Android. For me it's one of the best of the new Android's from 2015.i haven't tried any other Android for more than a week.
Ammitedly I have been using BlackBerry for 6 years but I have to say there was an awful lot of Samsung bloat ware I had to contend with on the S3 Mini.
BlackBerry just had the core apps what make it a Blackberry. The calender, the Hub and DTEK will be amazing when Marshmallow arrives when it can stop certain apps from using certain permissions. At the moment it just notifies you.
I would like to try the 6p, I think it's a great device but the PRIV easily closely matches it.
Regarding your concerns about heating and the battery, I have projections it can last well in to two days. I am a heavy user though and it drains much faster but the same would happen on an iPhone too.
The camera has received fantastic improvements in the last month. It really is one of the best on the market albeit the iPhone 6S probably is the best.
Finally I struggled to use the physical keyboard at first but I'm using it more and more. I very easily in a second can switch between swiftkey and the BlackBerry virtual keyboard. I think it's important to use a different keyboard for those incognito moments. I sometimes type with the physical keyboard with SwiftKey and I have asked them to add support for the scrolling track pad.
I recommend it.
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