IMHO, the Scubapros will be much easier to get serviced or can learn to service yourself
I say that as I recall hearing that Poseidon's are more expensive and there are fewer shops that do service Poseidons.
that's backwards. You can't service the Scubapro's yourself since you can't get parts for them in this country. Poseidon on the other hand actually has a class where you can be certified to repair them yourself and buy parts direct from the factory, but there is no restrictions in the dealer agreements for selling parts. Scubapro forbids it from their dealers, so you have to go to grey market to buy them.
The SP regulator is a known "quantity" with known excellent performance and a wide support/dealer network around the world. "Military Specs" aren't always relevant to the recreational diver or are current specs.
What's unknown about the Poseidon? The MK3/Xstream has been around a long time, close to 20 years for the Xstream, and over a decade for the MK3, though the basic design is close to 20 years old. The company has been around since the 50's and shows no sign of instability.
In terms of Mil-Spec, they're actively used by military divers, though I'm sure the scubapro is in a couple of navy's somewhere. That said, you are correct that being "mil-spec" really doesn't mean a whole lot, and I can certainly spec to that since most of my work involves things with actual mil-specs. I'm actually designing a product to one as I type.
@rhwestfall there are 6 Poseidon service centers in Hawaii, and the guy who runs Poseidon USA lives there half of the year so there will be stable shops out there for the considerable future.
Now, all that being said. I own all of the regulators in question except the MK3 first stage *mine are only mk2*, but I now have 8x Xstreams, at least 12 Jetstreams, 6 MK25's, and I think 4 S600's but they're getting sold. Only 1 G250, but 6 156's which are the same thing for this discussion. I don't use the S600's and would recommend the G260's out of personal preference. My normal setups are MK25 first stage with Poseidon second stage, and Poseidon first stage with 109/156 second stages. Why? The Mk25 has better hose routing for doubles and stages with the swivel turret and bottom port, but I prefer the Poseidon second stages. The Poseidon first stages are smaller, lighter, and have an OPV integrated into them so for my CCR, and deco bottles where I have an inline shutoff, I don't need to add an OPV to them.
@H.K.B. brand loyalties aside, pros and cons. The Poseidon will be a lot easier to keep clean and will be less finicky with rinsing since it is a wide open, flow-thru diaphragm cover vs the MK25 where you're going to have to be really careful about soaking with flow to keep the piston chamber clean. It's less bad than it used to be with the new ones since the holes are larger, but it's not like a diaphragm, especially the MK3 where it's wide open. Neither first stage is IMO ideal for regular salt water use because they are unsealed, but that is my personal preference. If you go with Scubapro, I'd consider the MK17 because it will be easier on maintenance for you, but the hose routing is not quite as ideal, though for single tank it's less important. In terms of which one you get, to most divers I would say get the Scubapro because it breathes like you will expect it to, but if you want a Poseidon, I really do recommend you go to one of those dealers and see if they'll let you do a try dive
