In reply to soeren:
Not sure what size the 2 person one really is, but I'd try and go for one you can get someone lying down in, as you'd probably want to be able to do this if one of you was injured. It's not a great problem if it's a bit big, you can tuck away the spare fabric.
I tend to take a plastic survival bag, too (though it's a lightweight clear plastic one, rather smaller than the orange ones) - gives you something dry to sit on if nothing else. But it warms up really quickly inside the bothy bag, they're really good. You don't really notice when you first get inside, but boy does it feel cold when you come out again!
Makes, etc - dunno, mine is home made and works fine. It helps if you can get one in a fairly light colour, then things don't look too silly inside. Mine's got a white roof (but red sides) which means people look normal colours, rather than strange shades of green, or blue, or orange...