Although Mares has a good reputation for regulators - I have heard of failures at depth - and in fact have experienced one myself. I had a Mares Proton LX that occasionally made a "popping" sound while underwater during the inhale cycle. Didn't think much of it at first, but once (and that was enough) at 80 feet, the second stage "popped" and from that point - no air! I immediately switched to my alternate - a Mares Proton alternate - which breathed fine and made a normal ascent. Later, the LDS informed me that they had received at least two concerns of the LX model making that "popping" sound. They were nice enough to make an even exchange of my LX for a Mares Abyss. So far, no problems with the Abyss, but following that little incident, I now use my older Aqualung Legend LX Supreme as my primary regulator and use the Mares Abyss as a backup regulator.