I've been using IEMs for about 8 years now, if you are responsible for mixing then using IEMs is tough, it can be done but tough, I always have a sound engineer mixing, so I can concentrate on just playing.

I can't imagine the possible hearing loss I could have had without them, I use custom molded ES60 Westones, even at lower volumes, there is still hearing damage at the those volumes, its physics,

The other problem with IEMS is that you can hear all the mistakes, and you can't play off the room ambience so it takes allot to get used to them