I have tried this recipe recently. Put it on a smoked half chicken. Wife and family loved it.
One trick, not sure if it is in the book (I have the recipe, not the book) but put it on the chicken after is is off the grill. Let it rest for 10 min then sauce again and serve, leave remaining for people to dip.
I read a magazine (Cooks Illustrated) with a white sauce recipe, that is simpler and just as good, and they recommended saucing off the grill.