I have the MK25/S600 for my primary, and an R-190 as my secondary. This set up works well and I have no complaints, except the 190 is not a cold water reg. I`ll be upgrading to a G250HP for my secondary when I get home. The G250 breaths the same as a S600 and is bullet proof—and it might save you a bit of cash. (I have MK25/S600s on all my deco bottles also)