Been running their weights for years in many sleds. Best aggressive upshift I have found. Tried many, many styles. builds track speed quickly and gets me up on the snow quickly with a killer top end push due to the 'tucked' style.
Only used the original style, not the newer "Drag-n-Fly" style, the original works so well.
Down side of the originals, you have to mod the clutch for clearance, so if that is not for you, I would look at the newer style.
Also, the bushings wear quicker with the increased performance, so investment in the $20 (or so) SLP bushing tool is a good addition to the tool box.