Wheel hub motors come in two forms. The majority are internally reduction geared to drive the wheel, but on some the motor runs at wheel speed so drives the wheel directly. That means a very slow running motor which for a given power is not quite as suited for hill climbing, though some makes have a switched high power mode to help with that. The main advantages of direct drive are simplicity, long life and silence in operation.What do you mean by direct drive - crank/rear hub?