Unlock with Apple Watch would be the only incentive, and honestly they're about a year too late to for me to get torqued up about that.
Not necessarily. I agree it'd be much better if it arrived earlier but remember, people who are vaccinated can still carry and transmit the virus asymptomatically. It's less likely but still possible. So the usual precautions such as wearing a mask and social distancing are still advised. I had the doctor tell me this explicitly yesterday when getting my second vaccine shot.
And the feature itself works flawlessly. Face ID has so far been 100% successful at working when I'm wearing a mask and using my watch to unlock my iPhone instead. There's maybe a half a second delay but that's it.