The benefit is real, both in noise reduction and efficiency gain, but the improvement in props in our RC planes would probably be mostly negligible. The reason 90 deg. bends aren't used everywhere and/or aren't bigger is the mechanical trade-off. Adding a 90 deg. bend creates significant CF induced moments in the prop blades, so you have to strengthen (read as thicken) the prop, which of course is not efficient- it's a trade-off that has to be evaluated for each design.

By the way, adding these bends to RC props is DANGEROUS for the reason described above. The props were not designed (the normal ones anyway) for the added CF induced bending stresses, so you risk prop failure by adding this bend.

DON'T DO IT!!!!!