I see you are a newer user here - welcome to Android Central!
I too just started using Face Unlock (along with the in-display fingerprint reader), and am also unsure of its security. I still prefer my in-display fingerprint reader.
I too wear glasses and I notice that my Face Unlock will work more efficiently when I have my glasses on. Maybe that's just a misguided assumption (maybe I use Face Unlock moreso when I have glasses on; maybe I go for the fingerprint reader more often; etc); but I too like that the Face Unlock seems to be picky about how it unlocks my phone.
Keep us posted on your journey with Face Unlock and how you are liking it!