The other thing about the US is that occasionally you'll find a police department that's willing to bend the law. They can make you touch the fingerprint sensor and then claim that they never did and they found your phone unlocked, and it'll be your word against theirs. If the court believes the police, which they are culturally inclined to do, the Fifth Amendment question doesn't even come up.

One of the neat things about encryption, historically, is that the government couldn't force decryption even if it were willing to break the law in doing so. That's why there were export controls and demands for backdoors in the '90s, and that's why there are demands for backdoors today. Fingerprint locks may mathematically involve encryption, but they don't have this property.