I have seen them used by helo pilots doing long over water flights over the north sea. They say that when the helo lands in the water there, it tips over immediately, generally faster than the can get out. The are trained to use the spare air before they hit the water, in case the cold water makes them gasp.
They figure they will get 3 or 4 breaths, hopefully enough to get out of the helo. With exposure suits they hope this is enough to survive....
I wish them well.
I have 19cf pony and a 40 cf bailout if I feel the need.
Do you have those pony bottles strapped directly to you while you're in the helicopter? Seems uncomforable to me.