When I had my 6s. iOS 10 betas almost doubled my battery life over 9.3.4/9.3.5. Same thing for my GF. She was getting 4-5 hours of usage on her 6s, that changed to 8-9 hours with iOS 10.0 betas. 10.1 improved my battery life on my 7Plus from 10.0.1. 10.2 betas seem to have improved it again. Not much but I can squeeze an extra 30 minutes out of the device, even with LPM off.
There is not one problem I can find that affects my day to day usage from 9.3.5 to 10.2. My device is extremely reliable. The only issue I have is an iTunes backup bug. But it's merely annoying and doesn't affect anything.