Is it worthwhile putting Propspeed onto an exposed propeller shaft?

I get the concept of the rapid water movement past the propeller blades keeping them clean and the importance of keeping a prop, particularly a folding prop, free of any growth.

But if the prop shaft only rotates at, say, 3,000 RPM, what is the advantage of Propspeed over normal ablative antifouling?

It's always been included in the cost of coating the prop but this year I've been stung extra for coating the shaft which has prompted my question to the Brains Trust.