I have Sim-1 XT+ and I am using it for bass and guitar. I am not into technical details, but it can make my Bongo or Stingray sounds like Jazz bass, Precision bass, Rickenbacker and they sound real with all minor things that are characteristic to those instruments. I even made test Bongo as Stingray and Stingray as Bongo and it is more than just EQ. And Bongo with a fretless Jazz sounds like actually fretless, the only difference is that you cannot make real fretless technique due to have frets. It is even more interesting - Stingray fretless sounds like a Precision bass with interesting twist.
I have not played it much with guitar, but I was very surprised when my JP7 sounded like real SSS Stratocater or Telecaster. Needles to say that all acoustic sim presets on JP7 humbucker are not even close to Sim-1, which is surprisingly close to the real mic'ed acoustic.
I am quite sure that is much more than just EQ match, but I am too short in audio effects to even try to explain. I can say that IMO Sim-1 is in the guitar sound imprinting in the place where Axe FX II with Quantum was for amp modeling. Sim-1 gives me a lot of fun and sounds convincing to me.