Looks and sound mostly.
You're not going to make enough power to outflow the cone. I've had both open and close top K&Ns and it's sound. The open gives more of a whoosh turbo-ish sound while the close gives a growling sound.
The open top cone does flow better but again when you're talking about 1200CFM and 1300CFM while you're engine only needs a max of 800CFM it's not going to do much for performance. (Numbers pulled outta my arse for example).
