You are right about that, but realize that this Tsdz2 is missing the clutch on the maingear.TSDZ2
tsdz2 tongsheng 36V 250W/350W TSDZ2 electric bicycle central mid motor torque sensor with coast/foot brake function
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I think better choice is TSDZ2 is better choice. ...
Also in the past all gears had straight tooth. (don't know, if that is still the case)