The standard e92 335i/335d use a single piston sliding caliper and vented disks with plain face, so the Performance Brake Kit would offer an immediate improvement in specification: Straight away you would have six pistons clamping the pads to the disk (instead of one) - giving better alignment of the pads to the disk, more stopping power and better pedal feel (especially if you fitted Goodridge braided hoses in place of the OEM rubber hoses). There would also be less chance of brake fade (if you use the brakes on track) due to greater heat dissipation across the larger caliper area. Last but not least, as the new calipers are made from aluminium you would also reduce unsprung mass. The drilled, slotted and vented design of the disks also offer advantages over the original plain face vented disks.
The only drawback about the kit is that the supplied pads are not really up to standard, for the brake kit to really come alive is to change it to Ferodos or Pagids