I got one for a few bucks a while back, just to see what they were all about. Nifty package, for emergency use. Pretty sharp edge with an actually usable length. Most likely, you'd be able to use it once, then need to resharpen. I keep mine in a mint-tin with some bandages, fish hooks, wipes, compass, etc. as an emergency kit. I'll never use it, as I'd always have at least one REAL knife on me, no matter where I end up.
Hey, if you can pick up 3 for $10 on the auction site, it may just be worth getting a few to throw into some places it might benefit you in an emergency, like your glove box, toiletry kit, or book bag, as long as you are sure not to forget it's there and take it on a plane or to school.