the main difference is in the first stage. i've been using the jetstream for years and the servo valve in the xtreme and the jetstream are identical. i also use a cyklon metal. tried the xtreme once. . .

it's the low profile of the xtreme seconds that makes the difference (and of course the first stage ball bearings in the first?)

cyklons, jetstreams, xtremes . . .they're all on the hi end. that's what makes poseidons different. they don't have entry level or mid level regs. and you're right, they're more expensive to maintain than your regular regs.

one thing anti poseidon people don't want is the gale force air that it delivers (specially the xtreme and the jetstream). some diver dont like it. me? gimme the jetstream anytime . . .