To be fair, this isn’t exactly new. In fact, voice unlock is a feature that was once present within Bixby when it was still new. You could set your Samsung phone to unlock with the “Hi Bixby” prompt, or set up other forms of voice passwords. These were removed at some point, and are merely making a return with One UI 3.1.
It also doesn’t help that it’s not exactly the most secure form of biometric lock. That award would probably go to the iris scanner that was last seen on the Samsung Galaxy Note9. Though with the current trend of having notches rather than bezels, that’s pretty unlikely to happen.