I opened the SRW wheel. But didnt take pics.
You are probably right that the br/thr use pots. But Im not 100% sure.
First I know the looks of pots (from building my own electronics).
But the 2 br/thr "sensors" dont look like normal pots.
As I recall there was 3 connections (like pots) but the 2 small br/thr "black boxes" could be some "magnetic" devices (like halls).
At least the resolution is higher than most higher ends potcontrolled wheels.
Conserning the wheelframe its made of pretty solid plastic.
But the central mounting nut is (as described above somewhere) made of steel.