I bought my Oyl Mountain (different from the Elite which uses aerogel) last summer/fall. Unfortunately it's been so warm in AZ this winter (I don't think the southern half of AZ got even a single frost night and today it's 93F!!! =/) that I've had only one or two nights around freezing. It worked great though, but I just haven't gotten a chance to really test it out and probably won't for another 6 months or more. Unfortunately that's also not a great apples to apples comparison since I've changed so much of my sleep system in the last year and half that there are too many confounding factors (with my new system I'm starting to think I'm a warm sleeper instead of a cold sleeper and that I just didn't know how to maintain warmth before).
For the weight there are probably better solutions that are more comfortable (Neoair XLite womens or XTherm, any DAM) with probably around the same general 4-5 R value in practice. For the price of $36 on clearance, however, I couldn't pass up having a cold weather torso pad on the cheap. I still probably recommend just getting a warmer variant of the neoair or a DAM if you can afford it and will spend a lot of time below freezing, but if you just need something for the occasional sub-freezing jaunt on the cheap the Peak Oyl Mtn is hard to pass up right now.
As for durability I used it frequently car camping with a SOLite CCF and so far it holds air fine and I haven't had any other durability issues.
EDIT: I realize my previous post was a bit misleading. For "much colder temps" I meant specifically that I had woken up chilled to the bone in 45F (albeit humid) in a 10F REI bag on an old RR. Swapping the RR for a SOLite and Peak Oyl Mountain could take me to around freezing in the REI bag (swapping my REI bag for WM 20F ultralite with same pad setup and I'm still sweating down to mid 30F temps). So given my new setup I would probably trust a half CCF for legs and the POM torso for mid 20s and a full SOlite pad + POM for down into the teens (I haven't seen colder than that yet) based off experience from previous frigid nights in my older setup in low 20F temps.