Very Subjective question here, but I just purchased a used Martec Elliptical folding prop that was beautifully refurbished at the factory. It fits perfectly on my 3/4" shaft (1970 Ericson 32 w/Atomic 4), but (during dry test fitting) as the blades extend, they hit the rudder and overlap the rudder about 1/2".
The advice from the Martec factory was to remove the shaft, have 1" taken off the front end, and then I should have plenty of clearance. The blades have lots of clearance folded and extended, it's just the transition that's troublesome.
The big reason for my propeller change is that the 3 blade fixed prop on the boat only let the engine get up to 1800 RPM and really bogged down the engine. I don't know the pitch, but I think it was too much for the Atomic 4. Another complaint with the three bladed fixed, is that the stern would travel 10' sideways for every foot backwards. The original two blade was sitting in a drawer in the boat, so I was going to put that on this winter and check it out until I saw the craigslist ad for this folding prop (12" x 6")
My question is: Is having a folding prop worth all the trouble of having the shaft shortened, or should I install the original two bladed 12" x 9" prop and sell the Martec? I don't race, but half a knot is half a knot, you know?