Hello Eric,
I am a member of the Poseidon fan club. For about 8 years in the 70s and early 80s, I dove servo-assisted side exhaust regs (Teknas and Omegas) and they were indeed the reg of choice for all advanced deep wreck divers here in S.Fla. At the time, I did not know about the Poseidon brand. The breathing characteristics of these servo regs were incredible amounts of gas delivered at any pressure and depth and effort. You could just not over-breathe these regs. They got better and better at depth and I dove them to 250' on air, on wrecks, in strong currents, and always had abundant gas supply. Regular regs just did not compare. They did have quirks. The Teknas would "chatter" shallower than 30' because of the design, and the Omegas were "wet" breathers because of how the exhaust was located, but that was easily managed and they were oh so worth it for deeper dives.
My gear was stolen in the late 90s. I rented for a while and about seven years ago replaced my gear. Teknas and Omegas were long gone and I did not know servo regs still existed, so I got Apeks XTX 100s. Very nice breathers, to be sure. About 2-3 years ago, Hollis announced the return of a servo reg, based on an updated Omega design. When I looked into it, I discovered Poseidon and that I could have had servo all along! So, I started considering a switch. I liked the Poseidon Xtream second stage much better than the Hollis, as it was smaller and lighter. Also liked it better than the Jetstream. Finally, because I deal with a lot of current, I liked the exhaust point to the side and rearward, so never any issues with freeflow. Also, I thought the Poseidon Mk3 first stage was a masterpiece.
I went ahead and took the plunge. Got a Single Tank long hose Xtream set-up from DGX. Two dives later, my Apeks were sold (thanks Scubaboard!!).
They breathed like a dream, like my old regs, but without the idiosyncrasies. No chatter in shallow water. Really, really dry breathing. Incredible gas delivery at depth or under heavy workload. Just like I remember.
However, these do take getting used to. It does take a slight effort to crack them, but then they will basically "push" air at you. If you really suck on them it will be like a hurricane! And, everything in between depending on how you want to control them. I have never seen a reg that allows me more conscious control over my breathing. On a leisurely reef drift, I can sip air with slow, easy breaths. In a current on a wreck, I can crank the effort and inhale deep and hard and will get all the gas I could ever want. The side exhaust is nice as well. Clearing them is, well, nothing because they hold almost no water at all in the second stage, a simple small exhale and the water is gone. I can't imagine actually having to purge one.
Maybe because I was so used to them, but my gas consumption improved noticeably right away. I will say, that there is not as dramatic a difference between them and modern traditional regs (my wife's S600 is a great reg and she still prefers it to my Poseidon), but, if you take the time to really master them, they are still my favorite.
As for which one to get, I prefer the Xtream due to its second stage design. Just my preference. DGX has great prices on packages for single or double tanks.
