You could try sabots, but I wouldn't pick any real fast ones. You would probably have better luck with rifled slugs. I think they were originally designed to give a bit better performance with rifled slugs. Then fully rifled barrels became really popular, and after that sabot slugs, then recently the newer modern sabots.

I honestly can't tell you if it would be worth 40 bucks. I have never used one, I never actually seen one other than in a catalog. I have talked to people that have used them and it seems a bit iffy. I have heard of guys that got better accuracy with a smooth bore than guys with a rifled choke. And the other way around of course. I would think it really boils down to how hard you look for the right ammo.

Putting it on a scale from 1-10 is pretty difficult because it would really depend on the particular gun and how well it liked the ammo you were using. Technically it should give you slightly better accuracy and extend your range some. How much and how far is hard to say. I have seen guys that claim accuracy as well as some fully rifled barrels with a smooth bore, so anything is possible I guess.

Paul