I always suspect that it doesnt work.
I have used some of the intake cleaning products and I do believe that they really work. As an example. I drove from Clevelnad to Chicago on one and a quarter tanks of gas with the fuel additive in the tank. When I made the return trip I did it on a little more than three quarters of a tank. I hit some rush hour traffic on the way there but I don't think that it can account for more than a quarter tank all by itself. I belive that it helped my fuel economy greatly.
That is exactly what I used and I was very happy with the result.