Well, 1 out of however many aren't.
Will yours, or his, be that 1?
Unfortunately, there isn't any way to know before hand.
Most work perfectly fine. More now than they did even a year ago.
What I do first just sort of depends on what's easier.
If you arrive and are walking through the lobby first, there is no harm in popping at the desk and asking them to confirm your MBs will open your room door. They have a way to check this. I have done this on several occasions to avoid making a 2nd trip back over there. If I've gotten my room number and I can go straight to the room easier than I can go to the lobby first then that's what I do. Or I've also opted to skip the desk if I've arrived to the lobby and found a long line, being willing to take the gamble that our band will work vs. standing in the line. Or at least 1 of the bands will work.
One of the times it's the bigger risk is when you've done a split stay and you are on stay 2+. Sometimes, things don't switch right when going from room to room and the resort has to manually make the switch for you. But for a single room/resort stay, odds are in your favor that your band will open your door.
So, inquiring minds want to know, did your bands work?