I would more or less echo 38th's comments, though in my case I was using it with my bass to warm up a solid-state bass combo in gigs. Obviously a roaring valve amp would have solved my problems, but the GT2 worked a treat. Excellent value for money. Whether it still beats out digital sims for realism, I dunno .... But that honestly doesn't matter a lot in a small pub-sized venue, IMO, and the GT2 certainly made that dinky combo sound a hell of a lot better! :)
And, yeah, I dialed in my basic tone and then then didn't mess with it a lot (in fact, since I was playing bass, I never really needed to mess with my sound during the gig and just left it alone once we'd gotten through the sound check (if any! ;)).