the mustard is a binder to keep the rub on. it cooks away leaving no taste.
Got to somewhat disagree here Mule...The Vinegar cooks away but the Mustard and Spices are there, granted it is minimal, but there in the background. Remember guys, it is all
#1 about the SUM of the Parts creating a special and delicious result. If you taste MUSTARD you used too much or not enough of your other flavor enhancing Herb, Spices and Ingredients that " compliment " the meat. This includes Brines, Marinades, Injections, Rubs and even type of Wood Smoke. Obviously Tastes Vary .#2..A1 Steak Sauce still is on the market...YUK!... Bottom Line any thing you like or can think of to add flavor is worth trying...Could be the difference to make totally Outstanding Q!...JJ