As others have said, they are rather fragile. On top of that, the foam tends to disintegrate within a year or two. I've always had free replacement oams from Soundman but it gets a little old with time.
For me they aren't very comfortable to wear. Either I push them into the ear so far that the little spikes hurt or they're constantly at the risk of falling out. My solution has been to incorporate a pair into a polystyrene head with silicon ears. Works nicely.
Then again, I don't record rock concerts.
Ralf