my mate had one on his 172 typhoon, had a very impressive spec on his bike and hitting a ton apparently, he said that he felt the difference when he took the boost bottle off. from wat i'v heard the only make the slightest differnce and thats on 125 cc and above
They do work, although its not a case of just bolting it on...They need to be setup with precise calculations etc... Hence why people who do not know what theyre doing are discouraged from using them.