you can find a visual comparison between the polaris one and the "breathe" one below:
i'm pretty sure the "breathe" (why is it ALWAYS in quotes?) is slightly larger than the norman hyde unit. get more info about it here.
EDIT: a google image search for norman hyde bellmouth shows that the unit looks pretty restrictive (about the same as the polaris unit). if you don't want to eliminate the airbox altogether, the "breathe" unit is definitely the way to go. otherwise, i doubt the norman hyde is much better than the polaris. see?