I've never played one, but I saw High On Fire live a few years back, in a small club, and HOOOOLY SHIT.....that was the loudest show I have ever seen, hands down. I can't even tell you if it sounded good....it was a wall of massive sound.
My other guitarist played one, I don't remeber the model. He said it was louder than hell but didn't have a lot of gain, and he plays stock Shiva which he thinks has plenty of gain. He also loves stoner rock which is why he tried it out, he wasn't real impressed. He did say it looked cool though.