[Closed Case]

Agree. There is a place for the oil type K&N filters. Usually racing or older vehicles with no or not many emissions and sensors. As mentioned above, the MAF sensor is extremely sensitive and a light coating of oil on it could give you a headache.

Also, the in-cabin air filtration has many avenues for crap to go thru and air to escape. It is a not a completely sealed system and a filter, IMO, is only good to keep the larger leaves/dust particles out of the blower fan.
Those 'charcoal' filters do diddly squat IMO. You will still get the exhaust and smells coming into the cabin regardless of charcoal or extra fine filter. Marketing at it's finest. If anything you will muffle the forced air. Just like you do not want to put too dense of a filter in your home's ventilation system, so too in your vehicle. The cheapest and thinnest is fine. Heck, vehicles back in the day didn't even have any filters. I check both engine and cabin filters at least once a year. I usually beat them against a brick wall to get rid of any loose particle. If the filter looks relatively clean after, I re-use it. Otherwise a cheap alternative at wally world has worked with just the same results.

This of course is my opinion. Spend your money as you see fit.

In Europe the charcoal cabin air filtres are successful on recirculation mode in heavy city traffic. If you use recirculation on A/C or heating it gives environmental relief from gasoil vehicles. The clean diesels with lower particle emission LSD since 2005 helped too. I find that in NYC or major cities in stop and go it chokes out the blunts, especially in NYC were huff puff the magic dragon is a common cologne. The stuff smells like skunk as they blow it out their window in bump-2-bumper.

No thank you.