I guess maybe I'm just trying to improve something that ain't broken. Mine is very smooth thru the whole rpm range. I have a model 4/912ul with the Kiev 3 blade. Leaf has this and it seems like a good price compared to the price that others are asking. https://www.leadingedgeairfoils.com/propellers/balance-master/propeller-balance-master-6-hole-prop-black-anodized.html (I don't know why this won't highlight.)(Not sure if this is the right one since it doesn't say 912)
It's cheaper than the coolant cap that I recently ordered. My flyin buddy, also with a model 4/912, has a rough midrange. He has a Warp Drive prop. Lots of work, even new carburetors haven't completely cured the problem. I'm really trying to spend some of his money hoping it will cure his problem. I think I'd probably get one myself just to insure mine is as smooth as possible. Should help the gearbox live longer too.