[PGT]

all discs are cast iron. if the M Sport kit uses two piece rotors, it will have aluminum hats bolted to cast iron disks. Since the rotor is the heavy part and furthest from the center of the hub, it won't make much of a performance difference but will have some benefit on how quick the suspension reacts. Basically, less unsprung weight is good but in this case, its not spinning weight so not as much benefit in braking/acceleration.

Now, the calipers being aluminum will also help but being larger, they're probably the same as a smaller cast iron stock one.

Bottom line - this kit won't necessarily have any weight benefits to speak of but it would be interesting for someone to put the stock parts on a scale along with this kit while they're doing the install.