I bought one this year before I went to the alps on holiday. Its about £110, and I've no idea if anyone else makes something similar.
* Its very hugging so keeps your warm fairly well.
* The materials are quite slidey, so your jacket is free to move about and its easy to get down the arms of your jacket. Basically your not restricted.
* The sleeves come off. I found this good when it got hot, like 25C+
* Does it work? To be honest its more like a thin fleece in terms of insulation. I found it very comfortable between 5C - 25C. Below that I wanted a fleece under my jacket and above, I reckon I would have been uncomfortable whatever.
I do like the idea and I think it gives a lot of insulation given how thin it is, which is a big bonus. I like the fact it works with my old sidi jacket very well, the collar goes up nicely inside the collar on the jacket and the arms dont quite go as far as my jacket which means they dont get in the way.

up from me. Just dont expect it to be some kind of magic garment.