Oh that sounds great!
I think just to set the POI isnt much dangerous because its only affecting the YAW control.
But setting HomeLocation could be dangerous if Smartphone gives u strange GPS coords.
But maybe you could check if distance between actual homeposition and new position from phone is in a plausible range.
Maybe for different situations (Driving with car, Walking, Cycling, swimming
) you got a different max allowed distance.
And otherwise you leave homepos where it was before.
Edit:
I did some testing with changing HomePosition manually at System-->HomeLocation. It seems when changing home Location copters position shortly jumps to the difference between actual HP and new HP and then goes back to correct position(see screenshot). This maybe could be a problem...