I bought a SA 2010 Snell not-full-face (whatever it's called) helmet a while back because I used stinky, wet, dayglo orange loaner helmets for 3 DEs and I was tired of the entire loaner experience. The helmets were in such high demand that I was required to drop it off after every session so someone else could use it. Ugh.
Full face helmets were just too expensive and I have an airbag, which was my reasoning. If I had a race prepared car, I'd have a full face helmet, full fire retardant suit, coolshirt, spare tranny in the trailer, yada yada yada