I have one on my '04 955 Sprint ST.
1) pretty much what you said.
2) I have been in -5 at Armidale, it had frost on it but was not frozen. Heat is more of an issue. In hot weather I cover mine with a small towell or my jacket.
Comfort;
This is subjective as some hate them and some love them. My wife and I love ours, I sold my stock seat to Harry13 a couple of years ago.
Yes it is more firm and this is a lot better than the soft stocker IMHO.
DaveM