I saw some of these at a bike show during Bike Week. One of the shows had my wife's nephew's (by her previous marriage) bike in the show. I talked with him and he told me the belt gave better performance etc like the above posts said. But he also said it's not for amatuers to ride since if you pants leg gets caught in it, it can get nastry real quick.
Some were OK some got real hot, H D did this on the Sturgis Models, had lots of problems, pretty hard to find one of these in pristine shape any more, Most had vented primary covers:s
I ran Phase 3 belts enclosed on a 64 Pan and a 76 Shovel. With a 32 tooth tranny gear and chain drive they worked great. More responsive and less chatter. On my Dyna its so smooth from factory I dont see the point. Still getting used to rubber mounted engine. It's a whole new world.