I guarantee that any differences you are seeing from that are a placebo effect. Those things are a genius marketing ploy for several companies (e.g., Tornado Fuel Saver) and unfortunately, a complete waste of money.Appo said:I have one od these, makes a difference!
Edit: These guys have even gone one beyond the tornado fuel saver - they are trying to convince people to buy 2 for each vehicle to save even more! 50% emissions reduction in an off-the-showroom-floor car? No way!