I switched ot the Mk 17 after using Mk 20's and Mk 25's. For doubles hose routing I really prefer the Mk 17.
I also prefer the Mk 17 for it's bullet proof extreme cold water performance. It survived a high flow rate test in 35 degree water at 165 ft for 200 minutes (the end of the test). In comparison the Legend Supreme (a very good cold water reg) lasted about 30 minutes before freeflowing.
Performance wise, the 177 scfm flow rate of the Mk 17 is more than adequate for any tehcnical mixed gas or deep air diving purpose and I have noted no difference in performance in the water compared to my Mk 20 and 25's.
It is a very good first stage and is in my opinion the Apeks killer that Scubpro has needed the last few years.
I am not a real S600 fan if it is paired with a Mk 25 as I dive primarily cold water and that combination seems to have a higher incidence of freeze ups in extremely cold water (40 degrees or colder). However, a frequent dive buddy of mine has used an S600 with Mk 16 and Mk 17 frst stages and has had no problems at all with freeze ups, compared to the several he had with the Mk 25 S600 combination on identical dives.
I am also a big fan of the G250HP. It offers performance identical to the S600 but for less money and it's cold water reputation is a lot better.
I have an X650 that has done extremely well in ice diving and extreme cold water diving to 150' and overall I prefer the design to the S600. It also won my very recent competition as to what second stage to put on my Kirby-Morgan full face mask. For whatever reason, it performed better than any other SP second stage I tried including the D400. So the Mk 17 X650 will be the primary reg for next season.
The MK 17 X650 is in my opinion the best regulator package Scuabpro sells at the moment and I cannot think of any regulator I would rather buy from any company currently.
