I have never used one of these and just wanted some feedback from you guys on it's uses in the studio?,,is it similiar to a tube screamer in tightening up the low end?
I don't think they are much good for tightening up anything. The Rat is more of a very fat and raunchy distortion sounds great on bass for metal and for guitar if you like the dirtier kind of sounds.
Try to get an old one, alot better than the ones you buy new today. I had both and the difference was quite clear. The sound on guitar is less buzzsaw than the HM-2 by the way, but these two complement each other greatly to provide one big wall of grinding nastiness hehe.
I've never owned one, but i saw an awesome grind band from Cork called I'llEatYourFace. was talking to the guitarist after the show and he used a Rat through an old Hi-Watt stack. it sounded great, and it was a drums and one guitar lineup too.