I have owned two BME twins and the only problem I have had with the single bolt hub is when using an aluminum spinner. The spinner backplate moves relative to the hub no matter how tight the nut is tightened.

My fix is to drill and tap (8-32) the hub at two places, 180 degrees apart, and install short socket head capscrews in the holes. Match drill the spinner backplate just larger than the screw head. This keyes the backplate in place with the hub.

Wood props work fine using this method. C/F props seem to require drilling through the prop washer and prop and installing longer screws through all parts to keep everything is it's proper location.

I mentioned this to Keith and thought he was going to incorporate the tapped holes in future production. I can't tell from the pix on the website if the Extreme has them or not.