Can someone please explain how a cold galvanize spray is going to inhibit growth on your prop if galvanizing doesn't do so on your anchor chain? Not that you are going to get a cold galvanizing spray to adhere to a bronze prop without using a very expensive etch primer, which is not a good thing to do to a prop.
We tried Prop Speed and it worked for a very short period of time. Certainly not worth the money. Bottom paint won't even stay on the shaft, never mind the prop, though it does stay on zincs and Dynaplates quite well, thank you boatyard painter guy.
In Oz, on the sport fish boats out of Cairns, we tried chroming our props (to attract fish, not inhibit growth). Even with the polished slickness of chrome and running almost every day, we'd still get growth on our wheels.
The guy (or gal) who does come up with something that will actually inhibit growth on our running gear if one uses the boat at all, will be one very wealthy individual!