Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Underwhelmed

For the price, I expected more than a half a mile per gallon increase.It will take about five years for this thing to pay for itsself, and I probably wont have my car that long. Maybe it is more effective with other vehicles, or maybe I set the bar too high. (After all, the Tornado is essentially a small piece of twisted metal.) In either case, I dont discourage you from giving this product a shot, I just dont endorse the decision.