I have used Cruiselineformal.com for the last 2 cruises on Princess. Works out great for me. One less suit to pack, 2 less shirts and not ties. Leaves more room for Scuba gear.
Seriously, the quality you get is very good and provided you take good measurements, the fit should be good too. I have rented the White Dinner Jacket and black pants. Comes with 2 shirts,tie and cumber thing.