The stock air box's design works quite well, good flow rate, and filter's the particulate very well. My concern With the K&N is simply filtration. It flows better, and over time the filter media does get weaker, allowing lots of particulate into the throttle body/motor.
On my motorcycle, where stage3 = K&N, Headers, re-jetting, I am on the 3 rd set of K&N's over 8 years. The recharger kits is nothing more than fine oil to help trap more dirt, that often does not work as advertised. Leave your stock air box in, spend the money on a good dealer emission /throttle body service, or something else.