Pilot DAR .... Interesting and though provoking post, it is always interesting here from people who have done a ditching including the Hunson River A320 incident, additional unexpexted problems always crop up.
I have to say, I have a redurbished RAF lifejacket, much better than most of the civilian likejacts, as it is waiscoat style with pockets, for personal ELB and flares. It has a larger compressed gas chamber, to give extra boyantcy, I suppose because it designed for use with an imersion suit and g-suit.
I am never sure, if part of your flight is going to be over water, why someone would chose to wear a likejacket at departure, there no really uncomfortable. It is really not easy to put a life jacket on in flight.
Next we have the problem in the UK is surrounded the North Sea, Irish Sea and the English Channel which at certain times the survival time is very limited, the RAF and RN only allow flight over water without immersion suits at certains times of year, It's tipicaly between May and October. Yet in the over the years, I can think of a number of fatalities where light aircraft have ended up in the English Channel and the occupants have perished in the cold water. I never understand why you would plan a flight over unserviable water without an imerssion suit.