I have only had it on chicken. Never on pork or beef. It is not my favorite but it can be okay. It is more of a north Alabama thing. Made famous by a place in Decatur Alabama.
Mustard/vinegar is very much the South Carolina sauce. North Carolina sauce is either Eastern, which is just vinegar, brown sugar, and pepper, or Western (or “Lexington” sauce), which adds a little ketchup and butter to make it creamy. Eastern NC style BBQ is the whole hog…“everything but the squeal” they say.
Not my first choice for sauce, but it’s actually pretty good, especially on chicken as you pointed out. I think the place you might be talking about is Big Bob Gibson’s BBQ.