The Scubapro Mark 21 is not in the evolutionary line of the Mark 20 to Mark 25. The Mark 21 is an odd evolutionary mutant, a dead end dodo bird that looks more like a model airplane engine or a miniature motorcycle engine than it does a first stage regulator. I think I would pass on it. But if it had two mint G260s or G250Vs attached I might rethink my pass.