Green is a lot louder than the K&N, like Jamie says its a pig of a fit and you have to make sure you get it just right or it rubs on the engine bay. It doesn't feel as well made as the K&N either but its a very good filter.

The K&N is much more subtle, better build quality than the Green and fits MUCH MUCH better - also comes with the cold air feeds.

I had both, ended up sticking with the K&N, not much in it - nothing in performance difference. Go with whichever you prefer the look of / noise of - both are great and a very good first mod to do - Jamie's guide is spot on - just make sure you get that fitting right before you start driving too much with the green or it WILL rub.