I bought one on eBay for our upcoming trip, but haven't used it yet. But, I've read many positive posts of others who have used them with no problem. I also have one for Baskervilles Restaurant in the Grosvenor Hotel.
I used one last week with no problems. The buffet did not look too good, so we ordered off the menu. I got the Ribs and my wife got the fish fry. They were OK. I don't think you would really want to go multiple times, unless you have many children.
We used a it in December with no problems. My son got buffet and ordered mozzarella sticks of the menu. They accepted it with no problems! The waiter knew exactly what they wore and accepted it without any problems.