I found an article on Popular Mechanics regarding these gadgets and thought that this info would be helpful to some members new to cars. So just click on the link to read the article.
The truth is, car manufacturers will install them in the vehicle if they thought it was beneficial. Of course, if the device will lessen fuel consumption yet damage the vehicle in the process (like some that tinker with air:fuel ratio and create high EGT's) they will not install these.