MFL = male flare fitting. The male side is called an MFL fitting, the female side is called a swivel nut. These have a plastic washer (integrated or separate, depends on the fitting) so you tighten by hand and then barely snug with a wrench.
It allows you to swap things around very quickly without having to yank hoses off barbed fittings (with can be annoying or downright impossible for stiff barrier tubing). Most people use them to quickly switch between ball lock corny QDs, pin lock corny QDs, sanke couplers, etc. I have them on my system and love them.
I've heard keg connection is great, I've bought some smaller items from Birdman and they were fantastic.