I've used both.. Heres my take on ' intakes '.
Mac - Its metal. People will say it gets hot and then heats the incomming air. I used digimoto and measured a whole 2 degrees of intake temperature charge difference.. whoopie, has no effect on performance. Didn't see any real gains in performance.. ' looks nice ', not much else to be said.
K & N - Too pricey. I think they used a faulty dyno in their testing as the alledged performance gain.. almost non-existent. I believe I saw all of 5hp? I already had a full exhaust on before the intake, I was expecting to see more.
Factory airbox, modded with a good air filter - Best way to go if your not doing a power adder. You already have the parts, buy an aircleaner. Invest the money into a good exhaust or an E-Fan where you'll gain in milage ( $ savings ) and there will be less parasitic drag on your engine. Its a win-win situation.