???? scratching my head here.
Cadence sensors, while they are cheap and comply with the law, IMHO do not give a good 'experience', regardless of the software behind them as they measure the wrong thing.
I appreciate that if you buy a ready made system, it adds little complexity. If you want to build your own, it does.
My interest in developing this is that I damaged both knees in a fall from height and while I can pedal, I cannot maintain a constant cadence or torque. I found it made a commercial cadence based PAS 'bunny hop'.
I've done a lot of development on torque sensors. They started with force sensors coupled to chain rollers, evolved to load cells measuring the flex in the frame and the best so far measures the stretch in the chain using a pair of inductive pickups and measures the differential phase of the chain rollers passing the sensors. A torque sensor with decent software genuinely flattens the hills to the point that you don't notice the hills or electric assist is there.
For me, the best experience though comes from a twist throttle. While my last build may have grandfather rights, my current build may not and I have to investigate the alternatives. One of which is a twist-n-go + IVA test.