Something to consider is the inability to remotely grant access to the safe. For instance-my brother is staying over, watching my kids. He has some reason for concern about their safety, and calls me.
With a simplex lock, I can tell him the combination and allow him access to a firearm over the phone. Never possible with biometrics.
Will this come up often? No. Ever? Probably not...but combined with all the other disadvantages biometrics have, taking access out of the intellectual realm and putting it in the physical realm is not an improvement, IMHO.