I bought several scuba items from a guy exiting the sport. Among the goods I received was a US Divers Conshelf 21 and an almost new Cressi MC5 Ellipse Black. I am planning to keep one as a back-up regulator and sell the other; however, I'm a bit on the fence as to which regulator to part with. I'm leaning toward keeping the Conshelf. Would appreciate any opinions offered.