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Ink, performance and battery life is fine. There are two in the house running 10.2. Ymmv though as acceptable performance is based on the individual.
 
My old spare phone is a 5s and it's been running 10.2 for weeks now since beta 1 of it. Battery life is slightly better than 9.3.5 in my opinion as a comparison. The only thing I will say is it seems slightly laggy at times on ios10, but I think some of that is to do with getting used to using an iPhone 7 so when I pick up the 5s it now seems slow in comparison. However turning on reduce motion got it back up to speed and it doesn't particularly feel too slow compared to the iPhone 7 generally.
 
Yes, we use two of them and they are on 10.2. I cannot say that I notice much of a difference since updating. The phones continue to do the job they were bought for three years ago.

The addition, through updates, of various bells and whistles all go over my head I'm afraid.

We have no wish for larger phones so have little interest in the 6 or 7 models, however, when I finally decide to upgrade, it will probably be to the SE or equivalent.
 
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