Had installed 2 of the K&N Air Filters. Since then I have been monitoring gas mileage.
In a 400+ mile trip to Maine, I averaged a shade less than 27 mpg (25 mpg used to be the best I could ever get). In another tankful of mixed driving, I averaged 24 mpg (22 mpg was my previous best)
All in all, I'm really pleased that I changed air filters at approx. 12,000 miles.
Thanks to the forum for making me aware of these products.