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.
That old man looks happy to have someone to care for him. Once he clears his FeLV and FIV tests and is dewormed I’m sure he’ll be thrilled to live inside.