I have just fitted a Tongsheng TDSZ2 mid drive to our Lee Cooper tandem. I imagine the process is similar to the Bafang. It was straightforward and I didn't even need to lengthen any cables. I agonised for a while about the difficulty of keeping the cranks in sync, given that the stoker's crank decouples as soon as he or she stops pedalling. I even tried bolting the stoker's timing and drive cranks together (now both on the rh side), until I realised that this completely nullifies the torque effect on the Tongsheng BB axle so you get no assistance. Now I have decoupled them everything is working well and it hardly seems noticeable when the cranks go out of sync. My stoker loves it that she can now stop pedalling whenever she likes, although this of course turns off the motor. I hope this all makes sense. I believe the Bafang has no torque response so I'm not sure how this affects the setup.