Using the chart in there web site and there figures, If you're getting 10 mpg now and saved their 4% saving, in 75000 mi. you would save 300 gal of fuel which at todays prices would be $1000-$1200. I don't know what they cost, but it looks to me the payback would be to long. I think they are made for the long distance hauler whatever he is driving.
Roger & Cheryl Full Time since 2002, RVing since 1975 2008 Chevy 3500 Crew Cab Dually, 2012 RW 36RL