In reply to O'Donopoo:
1) No
2) Depends on what you're laying on, if it's soft or snowy then it's not that warm because the snow fills the grooves on the underside, if it's a firm surface it's better, but it's hard to give a objective number as to what temp it's good for as it depends on a lot of things.
3) Yes, it's more comfortable although bulky.
4) You can get them a lot cheaper than £30, closer to £20 really and at that price you won't get anything better.