Its similar to the MX5mania CAI and the lock stewart CAI that plumbs into the firewall. Nothing wrong with it. Leaves don't make it into there and neither does water, if water did get in there, you'd be blowing moisture all over your face when you have the interior fans blasting away.
Mania claims to a small increase in power but it isn't really much to be very noticeable, although the induction roar and intake sound does sound awesome! Especially with some big cams and valve overlap.