Well...that was a failed experiment. The person at the check in desk wasn't happy that I left my 'phone number' as the one MVC knows...my home phone. And kept getting confused about who was in which room. And about how many keys I wanted for each room. Somewhat humorously, they doled out the pool wrist bands as if they were made of gold (as if I couldn't get as many more as I wanted by showing my ID and saying we lost them).
Lastly, they of course still wanted to see my ID and run my physical credit card. Which I actually prefer...it's just that check-in was delayed rather than expedited by my bothering to use the app.