When I first got into this motorized bicycle business, the very first thing that jumped out at me was the so-called 'rag joint' was, at best, a very last resort. It just seems like such a slipshod, haphazard way of connecting things, puts MASSIVE sideways torque on parts (spokes) that aren't made to take that sort of constant pull, getting clutch sprocket, chain and gear to line up JUST right is a major headache which also needs CONSTANT readjustment....
In short, get a hub adapter, make SURE it fits nice and snug and keep the rag joint in the back of the shed for a very, very, VERY rainy day......