MK2’s are Scubapro’s entry level unbalanced piston design. What that means is the intermediate pressure supplied to the second stages will begin to decline as the tank pressure drops, but with a nice balanced second stage like a G250 it is hardly noticeable. If you use the R190 as a primary it would be noticeable beginning around 500 psi tank pressure and the reg would gradually get harder and harder to breathe, but the upside to that is you get plenty of warning when your air supply is getting low.