I use the accelerator balls for a couple years. I used a chrono and was able to get 5 - 7 fps and they quited the string. That was on a 2 cam bow. I have purchased 3 single cam bows and did not gain any speed with them. I also tried the spider speed balls and after about 10 shots I noticed a wear spot showing up on my new winners choice strings I removed them ahd deposited them in the trash, I kepted the balls. I have heard from several others that some get a little speed increase and some don' t. Mark