It's legit, but why bother? Why not just go directly to the source and pay a lot less. Plus, you won't have to wait in line at the ticket booth at Pier 33 to exchange your voucher for a ticket. You can get right on the boat with the ticket you print out from City Experiences...
At the same time, the fees are insane, they limit honest reselling sometimes (I legit managed to get 2 sets of taylor swift tickets because both my wife and I were trying to grab them at the same time, and I couldn't resell - only transfer - on t...