With so many different fuel additives and oil enhancers out there, I still believe the only way to save gas, as you are driving, is to drive responsibly.
Many of us can not or will not give up the comforts of our mini vans or pickup trucks whether it is because of work or a large family. Neither can we expect people to pay an arm and a leg for one of the newer and more fuel efficient models. So aside from keeping up on the oil changes, correct tire pressure, and other maintenance pieces we preach about on this blog, one can drive in such a way that it does not waste fuel.
You lead feet out there...you know who you are... taking it easy on the gas and the brakes will save you a couple of miles per gallon. And it is cheaper than the additive you were contemplating.
Driving the proper speed limits also saves in gas...and avoids speeding tickets!
Abusing the brakes not only wears them down, but also forces you to have to apply more gas.
Bottom line. it is cheaper to adjust your driving habits and properly maintain your vehicle's fluids and tire pressure than compensating by adding unknown fluids.
The choice, as always, is yours.