I used them for the first time recently on some UK flights with BA and they worked fine. Does save a bit of fumbling around although I do tend to keep these inside my passport.
You do get the occasional agent who manages to press the off button on your phone though.
95%+ of people were still using paper BPs.

I do like them although for special flights such as getting 1A when flying international first for the first time, I would rather have a paper BP to show off