I've used K&N air filters in my vehicles for 30 years and have never had a problem with them and I've never bought more than one for each vehicle because I wash and reuse them. Some applications resulted in increased mileage some didn't - none got worse.

 

I also have used K&N filters for about 20 years or so on several different vehicles - some for upwards of 100,000 miles. I've never personally had any adverse engine wear or problems. I'd consider going to the green ones if the weave is tighter just in case, but I can say that I picked up 1-2 mpg on my '05 5.4 and a definite seat of the pants improvement in performance. The truck will respond quicker at WOT and crank up thru the rpms faster than it did with the stock filter. This is subjective seat of the pants and all, but I'm a skeptic and not snowed by hype or advertising. I really do think I'm feeling a detectable difference. The mileage has been consistent over time as well. I would agree with the theory that the engine can pull air in faster and easier thru the aftermarket filters instead of looking at overall flow capacity. Dusty and dry locales might be different as far as engine risks are concerend - the one truck I did used to run gonzo with when I was younger had the round KN filter with a pre-filter around it and that still seemed to do really well. Sold that truck with the same filter on it and 165,000 miles and no problems with the engine - strong as an ox and no blue out the pipes.