amascuba:
The Scubapro MK2 is an unbalanced piston regulator. they are simple, tougher than rocks, and are great breathing cheap regulators. They are a regulator that I would only use in recreational diving though. Being that they are unbalanced they will be tougher to breath at deeper depths.
I agree that the MK2 is simple and great breathing, but the unbalanced design of the MK2 has nothing to do with it's performance at depth; unbalanced regs respond to depth in the same way as balanced regs. "Unbalanced" means that the IP will drop slightly as tank pressure falls below 500PSI, and breathing resistance will increase. By the time it gets noticable, you'd be low enough on air so that if you're not very close to the surface, you need the "reminder".
I know for a fact that this reg will supply more air than any single diver could breathe at anything even close to recreational depths. Two or three divers huffing and puffing off one MK2 in an emergency, maybe that's a different story. It is also more freeze resistant than most high performance regs. The second stage it's usually paired with, the R190, is almost certainly not as smooth or as effortless as the higher performance apeks regs, especially at depths in excess of 100 ft, but don't let anyone tell you that it won't work well in the conditions you've described.
I've compared my MK2 back to back with my MK15/G250, which by anyone's standards is a very high performing reg. At rec depths (down to 120 ft or so) there is a slight but noticable difference in the ease of breathing, but its nothing like "damn, I can't get enough air".
We all tend to forget that most decent regs made today perform far better than we really need, and that divers a few decades ago routinely made very demanding dives with regs that wouldn't make it out of a pool by today's standards. Still, my favorite 2nd stage is my old balanced adjustable, probably made in the early 80s/late 70s.
