Oversized derailleur pulleys are all the rage nowadays. Big derailleur pulleys cause less deflection in the chain and slower rotations in the bearings.
Both lead to less friction and a more efficient power transfer between legs and wheels.
Kogel’s goal was to build a cage so stiff that it holds the chain like a stock cage, while offering all the benefits of low drag oversized pulleys.
Kolossos is 3x stiffer than the main competitor product and 2x stiffer compared to the original pulley cage on your derailleur