They sound great on guitar as well. It sounds very thick with a nice dirty edge, definitely great for more raw sounds (more the kind of pedal for use in post rock, grindcore or old school death metal than when you are planning on sounding like one of those millions of in flames/arch enemy clones hehe) . The distortion is pretty dirty and the normal rat already packs tons of it. If possible you can best try to find an older one, as from the two I've had and the ones I've tested I've noticed that the newer ones are unfortunately noisier and sound less alive.