I have the exact SOSpenders model Frank showed the image of; it's made by Stearns. Since I'm generally wade-fishing rivers by myself, I never go without it. Its "low profile" footprint means that you're not even aware you're wearing it. Frank does note that if you're knocked unconscious you won't be able to pull the inflated vest over your head, but then, if you're knocked unconscious by the fall, you wouldn't be able to pull the activation tab either. However, if you've inflated it, even with not yet having put it over your head, it should still keep you front side up.
As in everything, there's trade-offs. For me, I'm willing to trade off the bulk and heat of a non-inflatable or automatically-inflating vest for this model which is so easy to wear you don't even hesitate to wear it. While I do incur the risk of slipping and knocking myself unconscious in the water, I try to avoid those high-risk situations anyway so it's a risk I'm willing to assume (I'm a former
Paratrooper, so I know something about assuming risk
). I should add that the belt pack negates the need for the wading belt you'd normally be wearing anyway, plus allowing attachment of other tools like wading staff holster, etc. As for automatic inflatables, I get wet enough from rain, splashing, etc. that I wouldn't want a PFD inflating automatically on me in those situations.
One last thought for those reading this who - like myself - often have to fly to fly-fishing destinations; even though the TSA and FAA regulations have clearly for some time specifically allowed the transport upon commercial airlines in either carry-on or checked baggage of CO2-inflatable life-vests along with a spare CO2 cartridge, more often than not the TSA security personnel at airport security checkpoints won't be aware of this. Therefore, I always
carry it in my carry-on baggage along with a print-out of the current TSA regulation expressly permitting its transport on airlines. FWIW, on two of my last three trips I've had to produce that copied regulation before they'd allow me to carry it on (alternative would have been to throw away the $17 CO2 cartridges, making the vest useless on that trip). If anyone wants a copy of the current Federal Regulation allowing CO2-inflatable life vests to be carried on commercial airlines, just let me know and I'll e-mail you a scanned copy.