I must admit that I have recently been thinking of using one even though I just fly GA. Successfully completing a PFL only to then smack your head into the altimeter knob would be a very annoying way to pop your clogs. I would of course have to put up with some dodgy looks in the clubhouse but I think I'd cope. We always used to wear one in the UAS even if we were just doing circuits.
Due to head clearance in my aircraft I think I'd have to go with a HGU-55 which
AFAIK can only be acquired in the US. These guys seem to specialise:
Flight Helmets - Flight Suits - Aviation Helmets
I also have an RAF MK4A which I keep meaning to get converted to GA.