Oh my gosh! It's THE MogX! I hope to see ya around more. It's great to hear you'll be active! I liked your commentary, by the way. Hilarious!
Anyway, n-air is a very tricky move. It comes out as fast as F-air and U-air, which is 10 frames (I'm pretty sure). It's a good tool to use to punish someone while keeping them close by for a follow up since N-air has low knockback. It's hard to find thses situations though. Honestly, I use it to get pikmin off of me or my favorite, stop Falco/Fox's Illusion. I might be just me but I feel that I get better results from a nicely timed N-air than a b-air
. I has good enough priority to stop them dead in their tracks unless they managed to get through with their invincibility. The low knockback sets them up for a F-smash since if they land they get frame trapped with RCO lag and if stopped at the tip of the ledge they either eat that F-smash or air dodge to their doom (assuming they used their 2nd jump).
Meta Knight? Well... I'm actually not well veresed in Meta Knights KO percents. As for good random tips try to launch him up and bait his D-air and punish with U-air. If you can space it right, Kirby's F-smash>MK F-smash. If you see a MK charging one you can show him why it's a bad idea!!
Edit: *sees post above* Oh... I wondered where that comment went!