My primary use for my Neoair All-Season is alpine climbing. I wanted something light, warm, and comfortable. I was using a foam Ridgerest for a while, but at almost the same weight as a Neoair but less warm and less comfy, I decided to upgrade.
I bought a Neoair and the first time I used it, camping on a glacier, I woke up to a completely deflated pad. Should have tested it out at home first. I couldn't find a leak so I assume it was a valve issue; I probably just had a bad apple so I exchanged it for another Neoair. I used this Neoair a few times, including as my only pad on snow and glaciers, and it was actually sufficiently warm and certainly far warmer than a standard foam pad with the same r-value. I think Thermarest is being conservative with their r-value. I wouldn't want to use the pad alone in the winter, but for summer alpine climbing, it was surprisingly good on snow - not great, but definitely good. A couple weekends ago, I went on a very relaxed overnight trip where camping was on dirt. I blew up the Neoair to find out there was a hole in it from who knows what. The material used is just not that strong and not trustworthy.
I decided enough was enough and returned it, getting instead the Neoair All-Season. I had a chance to use the All-Season this past weekend and it worked great. Slightly heavier (5 ounces), but the material is the same thicker type used on the Thermarest Trekker pads. I was camped on dirt so I can't comment on how warm it will be on snow for now, but it kept me plenty warm on the dirt. It is also less 'crinkly' than the standard Neoair. Comfort is identical. The All-Season is slightly larger when rolled up, but it's not notably different at all.
This all said, I have a few climbing partners how have the standard Neoair and have not had issues with leaks, etc. and sleep just fine on snow with it, but for me, an extra 5 oz of weight is worth the added warmth and durability.
On a side note, the 'stuff sack pump' the Neoair All-Season comes with is worthless. I tried it this weekend and it would take ages to pump the pad with it. Like Thermarest says though, it might be handy in winter when blowing so much hurts the lungs. But for normal use, leave the 2 oz stuff sack at home and put your the pad in a ziplock bag or lighter stuff sack, and blow it up by mouth.
Hope this helps!