In reply to Fiskavaig:
As the title says they are a survival bag and not a bivy bag.
For survival you might want to think about the circumstances its going to be used:
Injured, collapsed and you or someone you are with are or cannot move until MR comes.
A Blizzard blanket would better since you can get it around someone without disturbing them too much and you can check on vital signs. Whereas a bag is a sleeping bag and getting a casualty into that can be a bit of a trauma.
Cold, can get off hill. One of your party or you find someone etc.
Blizzard Jacket which will cover down to feet but for movement can be tied up.
In both cases go for the Orange option if you can.
My only connection is our MR team uses them as do a lot of teams.