I dive ATX200s, and love them at depth, air or trimix. No problems over 3 years, down to 200'+. I also use Zeagle ZX50Ds under the same conditions. Good regs, although the 50D (with turret) is not a common tec reg, and I have had a turret O-ring blow once (on land, right after pressurizing). My buddy dives the SP Mk17 and Mk25, and praises them as well. My only concern with Mares would be availability of parts, not performance. In our shop experience, it is hard to find a time that Mares has actually shipped a complete order for whatever we were getting, and parts seem to be unreliably available.