You do need to be careful with two accounts . Have one on the phone and one on the desktop or laptop computer.
And dont connect your phone to either.
About Facial recognition-- iphone has this in the photos app other phones probably have similar.
My experience is that with makeup and hair being different this software does split me into more than three recognizable personas ... this can be a good guideline to know how fb might recognize you ... you can be more dramatic in your eye makeup or things like lip corners and contouri g makeup to throw the software off a little.