Normally I stay away from the fast food joints here. I find the cost to be more than the food is worth. I find that most have far too much grease and far too little taste.
The sauce put on the Big Mac is there to hide the dryness of the meat. The meat to me has little taste.
I'd rather do my own on the grill. That usually comes out moist without needing more of something else to hide the fact it's dry. Normally I grill them, at the last, I put around 4 slices of jalapeno peppers on top, then lay a slice of cheese over the top and wait for it to start melting. The cheese takes out most of the heat of the pepper but you still get the taste of the peppers.
It took being on the road so I am not at home to fix my own to realize how good a cook I am.