A must for when you are out in the water in a boat, canoe or kayak, it just makes good sense. This PFD is very good, I really like the one I have, it's adjustable and has a lot of pockets to hold just about anything; watch, keys, map, lip balm. I have attached a whistle to mine which tucks nicely into one of the many pockets.
It fits well, it's adjustable so you can get to fit to your body shape and the way you move, since it's light it won't make you too hot. This one is short waisted for kayakers so it's less buiky than some. The shoulders have plenty of cushioning on them, which makes it nice when you have to portage the kayak a bit; the hard bottom of the kayak isn't digging into your shoulder.
This PFD is Coast guard approved so no worries there, it will keep you afloat if needed.