Do you really need it? Do your brakes overheat that much?
The thing is - you could have some problems with rain and high speed braking (some newer BMW models have those problems, and usually they come to us complaining that their brake discs vibrate when braking when, indeed, they overheat the breaks while braking from high speeds and then the discs get very warm - and if there is rain the water cools them down - and you know that it isn't smart cooling down heated surfaces instantly - the material doesn't react good - brakes or looses original shape). So, be careful what you want.