K&N filters are fine. They're neither magical nor demonic - they simply offer a different set of compromises than factory filters.
According to independent tests for a GM Duramax application, the K&N drop-in filter traded 3.13% lower filtration efficiency for 27.13% less resistance at 350cfm compared to the AC Delco filter:
https://www.nicoclub.com/archives/kn-vs-oem-filter.html
That AC Delco filter costs $18.30 on Amazon. The equivalent K&N costs $69.99 plus ~$10 for a lifetime supply of air filter oil (you can use dish soap or simple green to clean). The AC Delco has a 45,000 mile change interval so in that application it takes about 200,000 miles for the reusable K&N to pay for itself from filter changes alone.