The frustrating thing about this is that people are already judging exactly how it will or wont work even though almost nobody has seen it working for themselves, and nobody except Apple employees has a face registered.
I do agree it seems like itll be more frictional (if thats a term) than TouchID but perhaps itll be fine. Perhaps we'll adapt.
I think giving the user choice is always better, especially if both choices work really well. But then again, Apple typically doesn't like to deal with redundancy and some of the design challenges may not have been worth it to them.