I've got a Forrest Dado King 8" set with shims that to be honest, I've used a very few times. Not because it's not great, but I've found that I prefer to use a router to make my dado's and adjust the piece to fit the predisposed slot size rather than cut a custom slot for a special thickness.
My Question how do you groove
1) Stack dado
2) dial-a-dado
3) Wobbler- (my first one)
4) Router
I'm considering getting rid of mine.