I was just on YouTube and saw this tool; I had no idea such a thing existed. The big negative to me is that it only tunes the indexing, or tells you if the derailleur or hanger is bent. It will not help you adjust the limit screws, or the B tension screw, or tell you if the cable or housing is bad or if the chain and/or cassette is worn out. Plus it only works on Shimano and SRAM 9/10/11 speed systems, sorry Campy owners. You have both 9 and 10 speed bikes? You need two separate tools. Just too many limitations in my mind for $39.00. I guess it might be helpful to some though, but to me? Worthless.