Some people like them, and some don't, but I run one. What they do, is keep the chain from compressing the back shock, which uses some engine HP. This is done, by moving the pivot point of the chain forward, so it's in line with the swingarm pivot bolt. It also does away with the stock chain rollers. It actually puts more HP to the back tires, now whether or not you have the tires to get the HP hooked up to the ground, is up to you. I run mine mostly in the sand at Little Sahara, and I can tell a difference. You will have to replace the sprockets once in awhile, and they aren't real cheap, about $70-$75 for both sprockets and bearings.