The minimum "legal" VLT (visible light trasmitted) is 35% and that is for glass+film - except for SA where the front driver and passenger glass must have a VLT of 70%. I know this because my car was defected for tint 3 times in the last few years but it just looks wrong if the tint isn't even.
I think the problem with metalized tints only really effect vehicles that have their antenna's etched onto the inside of glass, and this can be overcome by using a different film with a quality pigment. Ask the guys at the tint shop to explain further ;)
