The way I look at is, I save $500 to put towards something else I might want for my M
If you are going to install the hitch yourself, your total savings will be about $300. I bought my hitch, which comes with the two coolers from ACURA for $469.60 total. As I have an automobile related business, I paid resale price.
FYI, somewhere on this board is a thread that has downloadable pd. files showing the installation of both the hitch and the coolers. The cooler that is shown in your link looks completely different in shape then the factory coolers (transmission and power steering) it looks like it may block quite a bit of air that would normally be going into your radiator, some thing to consider. Good luck with your installation. Also somewhere on this board is a complete photographed installation by one of the members, might help you.