"I'm onto my second S5 (both second hand), why change from such a fantastic device?"
I agree, the only thing I could wish for is more RAM at times.
"The screen burn-in sounds like hardware failure that should be covered by the 2-year EU warranty. I've not heard of it from anyone I know with an S7 or S8 but it is known to happen with some OLED screens."
I suspect it's partly a case of user-error (at least for an Iphone that's what it would be), but what can you do if you need to type. As well she gets rather upset when I hint at that :P