Yes, my husband bought one of those things years ago and it was a complete piece of junk. You know when the instructions have words spelled phonetically, and sound like a Korean factory worker wrote them, you are in trouble. It did not do anything for our gas mileage, but did have a digital display that was supposedly the mileage we were currently getting, as we were driving. Whatever. Chalk that up to stupidity. The other replies are correct in that proper tire inflation, regular maintenance (simple oil change every 3 months/3000 miles) is your best investment.