well an easy way to tell is to look at the rear bumper and side skirts, the rear should have a open setup to allow air to pass, and the side skirts should have a slight arch in them to let air pass under the car creating a low pressure zone, this is the same effect that lets airplanes fly but in reverse:
see the slight arch of the side skirts on this supra:
and the up-pitch of the rear bumber on this exige:
andy's Combat kit is a ground effects kit, but it's not nearly as refined as the ww or xenon
if you want the best ground effects on a neon i would go with a Combat front bumber, WW side skirts, and a Xenon rear bumper, but that would be fugly as hell