As a 2 summer veteran of BK and 1 summer at Friendly's, I can tell you straight up : DON'T EAT AT THEM.
When the ingredients list for the BK onion rings stretches to 5 or 6 lines, there is something wrong.

There is a little hole in the wall diner across the street from me than I go to. I can stand at the take out counter and see right into the kitchen. It isn't spotless in there but it's way better than some I've seen.