I've used one before, and for freaks like me who need to play a breaking up 20 watt amp it's a saviour! The sound guy didn't seem to like it even though it was his boss's rig. He was one of those "I've been playing guitar for 30 years and that whole cranked amp thing is bullshit!". Uh, what?
I'm okay with people not wanting to play loud -really! I was in a band that required everyone having a really low stage volume, and I used an OD pedal and kept my volume low. I wasn't going to be playing feedback jams or any sick shredding.
Was I crazy about the tone when playing low and more volume actually coming out of the monitors than my amp? No, but that was my gig at the time.