I guess the logical question is "what mic do you use with it?"
As I understand it, Roland's modelling technology is very good for guitar effects, and for reverb, which are fairly coarse effects.
The differences between many great condenser mics are fairly subtle, and it kinda assumes that you'd have to use the very best mic to calibrate the Roland unit (wasn't it an AKG C3000 mic or something which Roland used? - my memory is poor), then subtract from the signal which is presented. It also assumes that the electronics in the Roland unit are pristine/transparent.
It sure won't turn a Shure SM-58 signal into a Neumann U47, I'm betting.
Is it worth paying for a signal processor which mostly acts as an EQ, and offers quite subtle changes to signals?
Does the Roland unit produce pleasing and discernable results?
I'm keen to learn more about it.