Going slightly off topic, I've had a reply from the RNLI who sent me some DVD videos on the life jacket design and usage.
One major factor in drowning Vs surviving is having the jacket correctly adjusted so that the head is kept out of the water. Jackets are designed to work correctly at a certain angle to the body to maximise the mouth/nose clearance from the water and a loosely fitted jacket will drop your cakehole into the path of every wave. The FAA/EASA line of requiring clip/adjust types makes perfect sense in that the jacket can be adjusted (tightened) to keep the bladders from rising up under your chin whereas the strap type, if not put on correctly, would be a total PITA to adjust. Also, having it tight to the body will preserve body heat. Food for thought?
As and when any other pertinent info comes In I'll post it here. Might be useful to someone, one day.
PS. 10,000 hrs 757/767 and 8 years CRMI.