I just get error messages. I've stayed at three or four Marriotts that had the functionality and even popped up the notice in the app to get the digital key, but it either never arrives or just crashes my app. Happens on both a Pixel 3 and an iPhone 6s. So I've literally never actually seen Marriott's version in action. I've tried uninstalling and reinstalling multiple times.

I used Hilton's digital key all the time. I love it for arrival - going directly to my room without a stop at the front desk is a huge benefit. If I want a physical card, which sometimes I do, I know I can just ask for one whenever I pass the front desk later and there's no one else waiting for a clerk. Hilton's version occasionally has a snag - getting into pool or gym areas is one that's bitten me before - but overall it's reasonably good. At most hotels, the time it takes for the phone to open the door is about the same time it takes me to walk from the moment my phone is in range (and I can tap the green icon) to the door itself. So it does not feel like a real delay to me.