I had read good things about them on another bboard, so gave them a try for Boston Citypasses this year. I had to bid on several auctions before finally winning a set.
They were absolutely a pleasure to deal with. No muss, no fuss. The passes arrived in lightning speed by an expedited carrier. The charge to the credit card was exactly the amount it should have been. The passes were just as described.
I wouldn't hesitate to use them for a trip. The only negative remarks I have ever seen about them related to cruises. Just be sure to read ALL of the listing thoroughly as there are fees for various things such as certain dates or larger sizes or better hotels.
Sheila