Don't bother with them! The will make the cooling to the front brakes worse, and they will also affect the airflow through the intercooler, and the engine air intake - bad sh!t - why do you think that VW never actually fitted them! 
how come vw sell them then if they are that bad?
VW 'designed' them initially for the 'hot climate' specifcation, which was supposed to have an additional coolant radiator behind the left grille. However, these were NEVER put into production by VW, for a number of issues. Firstly, the standard radiator, even in the hottest climates (Mexico, South Africa, Australia, Southern Europe, and even the Middle East) NEVER had this hot climate package fitted. Secondly, as I stated above, these actually take air AWAY from the front brake cooling ducts, and they also take air away from the DSG ducts.
The reason you can still buy them is simple. When they were first designed and initially signed off, VW would have ordered a few thousand, maybe more to be manufactured by sub-contractors. But when these were then 'cancelled', VW would have sold off the vast majority to the 'highest bidder' (the likes of Fischer Motorsport, and OEMpl.us) which in reality would have been a knock-down price. They would have probably kept a very limited stock in reserve, probably for peeps who genuinely needed to retro-fit the additional coolant rad.
