Thanks for this excellent comprehensive summary.
Very timely as I have just updated from wearing a buoyancy aid, which I never found comfortable and which had no crotch strap so tended to 'ride up' so probably wouldn't have been very effective in the water. I spent quite a bit of time researching what was available, there are certainly plenty of makes and options to choose from! There are videos of in-water tests run by RYA and others on YouTube.
There were several functions which I felt worth having, such as: automatic operation (with manual override); fast turning to keep you upright in the water; inflatable chin support to tilt your neck back and keep your airways clear; and a spray hood to help keep waves off your face. Finding one with all this but without being cumbersome was the challenge.
For my most common SIBbing scenarios I ended up deciding to go for a Crewsaver ErgoFit 190N Coastal Lifejacket with Hammar+ (with spray hood and water activated light) plus a Safety Knife (for which the jacket has a pocket and cord) and a Rearming Kit, ready for the inevitable time I slip and fall in at the slipway . . .http://www.crewsaver.com/Leisure/p/536/ergofit-190n-cs#
The best overall deal was from Marine Super Store and their service was excellent. Delivery was free, I ordered it on a Monday evening after 7.30pm, it was shipped on the Wednesday and arrived on the Thursday, with on-line tracking keeping me advised when it was due.
When it arrived and I unpacked it, I was concerned that it felt quite a bit heavier than I was used to with the buoyancy aid. I thought it might have been cumbersome, however having worn it for several hours on the water over the last few days I can honestly say it lives up the the maker's promised comfort level and ease of movement, much, much better than the buoyancy aid had been, especially when fishing. You really hardly notice you're wearing it, in fact I was part way through packing up the SIB today when I realised I hadn't taken it off!
I hope I never need it in a serious situation but it's good to know that if I do it's well up to the job and could save my life.