Shows the servo motor and cogs which changes ratio on variator which normally done by roller weights and centrifugal force this controlled by the ecu

Does anyone know why the delicate little cog in that pic is plastic rather than metal, it doesn't exactly look durable?

All that stuff bolted together and run dry for the life of the bike. The primary sealed bearing has been modified a few times, you can see that in the photo.
But it does work well and can last without problems on the vast majority of bikes.