it's only turning due to the wind pushing on the surface of the blade and not from the aerodynamic shape of the blade. It won't be so much as to be a problem using the switch. I'm thinking mine is running at about 40 or 50 RPMs in a pretty good wind when I have flip the switch. I had an old "Red Wing" 25 years ago with a 5 foot 2 blade prop that I would tie off with a line once I got the damn thing stopped. It was to dangerous to get close so I would short the windings at half speed which is all the slower I could get it to go by turning it out of the wind. It was pretty exciting but it never seemed to bother it much. It made a hell of a lot of power but it was prior to regulators and would boil your batteries if you weren't careful. The new generation generators are "Oh, so much better".