I looked into this ages ago for my first car (Fiesta 1.1LX Auto
) - they do work according to all reviews and tests I looked at, which were across a variety of cars. I installed it and the car did seem to run smoother.
Really easy to install, and a very well made piece of kit - if £50 is burning a hole in your pocket and you fancy fiddling with your car, give it a go - can easily put it back to standard.
I don't normally get sucked in my "snake oil" scam products - I did my research on this one and wanted to have a play under the bonnet, so bought it.