I have an old Rockman, I rarely use it. It does not transform my Electric guitar into an Acoustic, but it does create a palette of timbres that one does not get otherwise, and, like any other effect pedal, used in the right dose, in the right place, one can get some really usable sounds using one, for example; a good chugging background carpet that separate itself from the mix.
I also quite like it with piezo-pickup acoustic guitars, where it can help to optimize the sound, also, my E-mandolin sounds not too bad with it either.