Update: Pokémon Go continues to frustrate. Constant crashing and glitching which get REALLY bad if you share a connection.
There are games on iOS that are much more complex logically and graphically with a fraction of the issues -- this is simply poor coding on the part of Niantic. The good news is there have been many updates , the bad news is the problems continue. This app needs bug fixes over features right now.
Tried and consistent on iPhone 6 Plus, iPhone 5 and iPhone 7.
scottsimon about Pokémon GO, v1.39.0