since i have had the er-15's i wear them all the time in a club whilst playing as well, i havn't really had any problems with over compensation or anything either. To be honest when you use these it's nothing like using the normal cheap foam type plugs you get a very different sound to those the only sounds you loose is the very very harsh high frequency's (you still hear all the hats and everything fine though) and they reduce the volume by whatever level filter you have,although it do's seem to be important which db filter you get with them.
hope this helps , dam im sounding like a sales guy here