The Bafang M600 has had some teething issue's, it's first version had plastic gears which failed under hill climbing high torque situations, so they switched to steel, that caused another problem, noise.
Another company developed the solution, a PEEK plastic gear, strong and way less noise. With this PEEK gear, you have one of the better motors out there silent and powerful, and not as heavy as the ultra but still at 120nm. I have seen 120nm mid-drives climb some big hills, this motor is worthy of consideration.