Yes, thanks for posting that link. So it's a trade off. you can get various thickness bolt on hubs to the existing strut but that will limit the rotor and brake size, unless you get the brake adapter kit.
the link off r3v. is cheaper then the hub set up but you then will need to get e36/46 brakes. I would imagine with the rear m3 hub and bearing you will also need the backing plate and adapters for the brake calipers?