Never owned anything but hub motors, but let's say the mid drive motor is pulling you along. Now there's some chain tension, and let's say that the trike is equipped with a deraileur on the rear wheel. Then we go up a hill. Now we want to change gears to something lower so as to maintain speed. So how can we shift gears without a jerk on the chain system? Do we have to throttle back on the power to take the load off the deraileur to avoid yanking into the new gear or how does that work? I think the mid drive motors are built around the cranks and they can sense the cadence, but unless you temporarily reduce the pedal cadence or force somehow, the chain would feel the crunch.
But a hub motor will over run (reduce) the chain tension if there is more throttle added. This puts slack in the system and assuming the pedals are spinning a bit, the deraileur is happy and goes to whatever gear is selected- just like it does on the bike stand when you are testing the shifting. Of course you may or may not be adding to the bike's progress unless you once again have selected the correct gear, but you are still going up the hill and the chain never sees any abuse.
