I'm a fan of FB login. In practice it's pretty trivial to maintain once it's set up, I don't recall ever having to do any updates to an FB login system once set up.

It's nice that I don't have to create yet-another-password for a new app as well. I use a password manager so it's not a big deal for me, but for other users it could be so they may just use a shared password and having FB login would be a way to have them not do that.