Mark,
I know the Poseidon regulators quite well and the latest model (Xstream) is really the best regulator you can take with you under the water for deep diving. It is reliable, strong and has all the benefits of Poseidon's long experience with other excelent regulators, in particular the CYCLON model. In fact, the design of the 2nd stage has always been revolutionary at Poseidon, they never followed the other manufacturers "traditional" design. Poseidon's main characteristic has been the reduced size of their second stage and very solid 1st stages, ideal for diving in cold waters and extreme conditions. Accordingly, Poseidon is used by the German Navy, the US Navy and, of course the Swedish Navy.
Having said that, the only problem you can have (as a owner of a Poseidon) is if you live outiside Europe or North America. Then finding reliable maintenance (for the annual inspection and repairs) for Poseidon in Latin America can be a nightmare and a very costly experience. I am living in Brazil, here it is impossible finding spare parts or servicing for Poseidon. The only other manufahhtcturer in the world following Poseidon's concept and design is OCEANIC, from the US. In fact the OMEGA II model is almost a copy of a Poseidon, both the second stage and the first. I have two OMEGA II (with the DX-4 balanced diaphragm first stage/300 bar DIN). They are excellent and have been produced by OCEANIC, with this same design, for more than 20 years. At the end of the day, the quality of a reg is mesured by each and every diver under the water; when you breath very easily and you don't need to carry a heavy first stage in your mouth, then you know you got a goog regulator. If you want a very good regulator, but you live in a country without Poseidon authorised dealers, then the OMEGA II is the best for you (but you need the DX-4 Balanced Diaphragm first stage/300 bar DIN).
