This is a great service, I have used this on three occasions to buy show tickets and tickets to exhibits. This really saves you a lot of money, in some cases 50% savings on a show or an exhibit.
The only downside is there always seems to be a long line to get the tickets, and when you buy your tickets you don't get a ticket, just a voucher which you have to go to the box office of the show to exchange for a ticket. The only problem I had with this is when I went to see an exhibit, waited in line for a half an hour for the voucher, then went to the actual exhibit and had to wait for another half hour for a ticket. But with the savings you get it is worth the hassle.