Here's another mid-drive that actually has a torque sensor, the TDSZ2. The guys over at ES have started testing it in the real world and tearing it apart to look inside too. It appears to be noisier than the BBS02, but some like the torque sensor power application better. Here's a link for their discussion:

https://endless-sphere.com/forums/vi...p?f=28&t=79788