This is a SCAM. This product is a total waste of money! Not only that, it endangers the engine on your string trimmer!
Yes, it allows the engine to operate at much higher RPMS than designed. Two-stroke engines are inherently good at higher RPMS, however, when they design these products (i.e. Piston's sleeves) they use the least amount of material needed for the stresses of the designed RPMS and loads. So not only does it not work, it is damaging the engine you attached it to!
Please save yourself the hassle research stuff before you buy it. I research everything, but unfortunately, my father-in-law doesn't, and it ended up on our string trimmer I'm not happy, and now he can't find the original string trimmer. Now I have to spend 40 bucks for a new string trimmer attachment. I might as well go buy a brand new trimmer.
Bottom Line: No, I would not recommend this to a friend