OK, I would say MK is reasonably well known these days. People might say "Who?" if you mentioned him, but then you would say "The guy out of Dire Straits" and they would know. I would say MK is about as well known as Tom Waits, Lou Reed, Van Morrison.
GF isn't known at all, except within muso fan circles like us.
John McCusker is very well known in folk music circles, but not really known at all in the wider community.