The rotor in the kit (which one day I hope to have), is larger than normal. I have seen the one on prime. My thoughts;

The one on Prime uses the standard caliper. This in itself is not a problem. Most 4-pot kits use pistons which are the same size as the standard caliper, so they don't have any hydraulic advantage. However new calipers are lighter, take a bigger pad, and are possibly stiffer.

I see nothing wrong with the kit on Prime, apart from the price. It's a little expensive for a rotor + bell + caliper bracket. Also the rotor has to remain at 28mm thick, while mine is 32mm.