Looks like these may be them. I also would be concerned about the drilled holes handling the stress and heat. The description on the website alone is scary enough (IMO) given it only emphasizes the reduction in weight and then later mentions some tracks may not be suitable for this rotor :xyxnervou
if its a stright line drag car then it makes sense ,less unecerry mass on the wheels, and they look like they are on the back, most of the real breaking is done by the front , the only reson cars have rear brakes is to keep the back of the car from moving faster than the front...i.e. they keep the back of the car from swinging out then you hit the brake.