It sounds like it really is a situational issue. A group bag will work fine so long as you are able to get in it. There've been times when we discovered a little too late that not everyone would fit under the tent fly. Guess who drew the long straw. I would've prefered at that point to have packed an individual shelter instead of hodding that fly for everyone else to enjoy, while I sat up in the rain all night. Sometimes it sucks to be the biggest guy.

The simple mylar bags like Coughlan are not worth comparing to the Bothy. Bivy shelters (more like individual pack tents) aren't what I had in mind, my apologies for not delineating earlier. What I am looking at is the $30 Adventure Medical bivy bag that is also vented, but has far superior construction than the mylar junk. The Land Shark system looks even better, and for $60 is probably as good as you can get, short of an "Enviro" suit.

I'm not gonna dis the Bothy, but realize that they have some limitations as well. If I am looking for something to throw in the boot of the car for the whole family to use, I will pack a tent instead. If I am tethered to a party crossing a glacier and a storm hits, then the right size bothy bag is going to be mighty desirable. If I am out hunting elk or looking for a new cave entrance, I will take a bivy bag.