it more useful in the back than in the wrist
Only if it's like YotaPhone.
Edge screen already looks hideous.
I can go with dual front screen, but wished it was at the bottom instead of at the top.
Back screen is, meh. Other people can see what you're doing with it. And it consumes some part of the internals, and wastes them instead of having larger battery or more RAM or better camera hardware.