Scangauge, is it worth it for me?

[1cheap1]

Just logged 48.5 combined mpg. Cost of Scangauge is $170.00. Gain in using the Scangauge about 3 mpg? If so, $170.00 divided by $3.69 is 46 gallons. 46 gallons times 48.5 mpg is 2231 miles. Gain would be 33 extra miles per tank of 11 gallons on fill up, then need to fill up 67.5 times to reach break even point. 67.5 x 533.6 miles is 36018 miles. Add the 2231 miles of gain brings the total miles to 38249. I am going to drive about 8400 miles in this car this year. So it would take me about 41/2 years to reach the break even point. I am 63 years old so i don't know if i will drive this much in a couple of years. I may even drive this car a lot less. What do you think? Is it worth the expense?