Used it for about 2 weeks and noticed no significant affect on battery life, ended up turning it off because when it doesn't recognize your face the time delay to unlock the phone was too long. Plus I could only get it to recognize me 60 percent of the time, when it worked it was awesome but couldn't deal with it when it didn't.
I just set up my security last night. So far so good. When I'm wearing my shades, it obviously doesn't recognize my face. I'm curious in knowing if it will give my sister access since her face is very similar to mine. So far though, its ok but I will most likely stop using because its too time consuming when it doesn't recognize me.
I used it for like the first 3 weeks I had it. I loved it. Recognized me in most situations. Even in bad lighting. My brother like just like me. It still didn't unlock for him. When I had my beats on or glasses it still recognized me. The key to getting it to work right is to make sure the picture you take for it to compare to us in perfect lighting. Not too bright. Not to dark.
The only reason I'm not using it now is because I'm using go locker which doesn't work with face unlock.
I've been using it recently. I too am curious about it's impact on battery drain. I've noticed though, the trick is to train it properly. Every time it can't recognize you, go in Settings, and click "Improve Face Unlock" and have it capture your face again. I've done that a couple time and now it unlocks my face 99% of the time, even if I wear shades, a tuque, beard, no beard, etc.