I've been using them for years, they're great, I've also used a belt type that requires you to push it back over your head once it inflates, it's more comfortable, but wouldn't provide you the protection you need if you're unconscious. The one problem you might see is unintentional inflation, all of those I've used have a tablet that dissolves immediately when it gets wet that triggers inflation, my wife slipped off the side of my cataraft at the take out, she sat down on her butt in a foot of water and instantly had an inflated PFD....much to here surprise!!
The rearm kits sell for less than $10, include the tablet, pins and gas cylinder.
Tim