I got an answer from Doyle at Rad:
"The Bafang that now comes on the RadRover is a new hub motor made specifically for fat bikes. This motor is made with extra wide nylon gears to maximize the surface area of the gear contact points to handle higher torque. When we first started production, this motor was not available so we went with the Hengtai due to the torque capacity provided by the metal planetary gears. The Bafang company is a more reputable brand and the motor is quieter and requires less maintenance (no need to refill the oil bath and no risk of running out of oil). "
