"At 13 ounces it is definately the lightest full weatherproof shelter in existance."
I don't think that is necessarily true. I don't have a blizzard bag, and it does sound like they can work, but I do have a bothy bag and I think they are better emergency shelters and they are clearly lighter.
A two person bothy can be as light as 8 oz (terra nova or brooks range); the 4 person is under 16 oz. They are really tight, so that is more like 1.5 person and 3 person, but in any case, very light, 4-8 oz per person. The 2 person would provide plenty of room for one.
For an emergency, I would much rather have the room and ability to cook, or change, or dry out, or tend to injuries to myself or others, or repair gear like my ski bindings, full protected and warm in the bothy, then laying on the ground stuffed inside the blizzard bag.