First of all I would like to say that not all self-inflating airmats are made equal! I have had the Stormlite for about a year now and it is now not doing the job I bought it for. Let me explain.
This was the first self-inflating mat I had ever used. As a consequence I hadn't really noticed how well (or not) it worked because it was way better than my previous solutions! To cut a long story short, the last few times I have used it I have been cold. Now, some of this I put down to trying out a new sleeping bag (which I will review on another occassion) which was getting the blame for my cold, sleepless nights. Luckiliy someone suggested that it might be the sllep mat - so I put a blanket underneath the mat and ended up having a much better night's sleep.
Fantastic! Now this mat, in my opinion, is not up to scratch when used in late autumn. It seemed to be reasonably OK during the hottest months but even then I got chilly on some nights. I do run 'cold' most of the time. I have bought myself a Thermarest and will report on how it fairs when I get the chance to use it next.
So there you go - cheaper is not always better. The Stormlite was less than half price compared to the cheapest Thermarest and I now regret having been influenced by price rather than functionality. Lesson learnt!