Well, there really are 2 key things that are different. First, the internal invisible EQ that Bob does on all of the effects is tuned to his ear for either guitar or bass. Tweaking the 3 band EQ can overcome this to make a bass version sound good with guitar as ZWK has noted. Second, (and this is really the biggie) the guitar version has a "voice" knob and the bass version has a "mix" knob. If you are going to use this for bass at all, then you want a mix knob for sure. Are you going to miss the voice knob if you don't have it? Probably not so much. It is really there to help guitar players have yet another parameter to tweak and geek. I suspect that bass players will have a slightly better time using the bass version with guitar than guitar players will have using their version.