We were on DCL's repositioning cruise through the Panama Canal last year and rented his tux through DCL. We were pleasantly surprised at how nice the tux was!!! My DH got plenty of use out of it since the cruise was 14 days. I highly recommend them!
Although we didn't go with the option, everyone that I spoke with about the tux rentals for last year's cruise was supportive of using cruiselineformal. They were all pleased with the quality and convenience.