Has anyone here had success with USB fingerprint scanners?
I also found this Microsoft keyboard with fingerprint reader but I don't know if it works with linux.
More secure legally. You generally can't be compelled to disclose a password that incriminates you (unless it's already apparent that you're guilty of wrong-doing) but a thing (physical key, fingerprint, etc) isn't protected in the same way and can be demanded by the court.
Whether biometric are secure or not is another question, they can be stolen like any other data or a motivated attacker could just take you or your fingers.