Sensorless have more complex software for running the motor, sensored based systems are the easy way out as you don't need as good a software to run the motor. Sensor based systems should therefore be cheaper then a sensorless system. My U-Force 75 is sensorless and has no cogging with my Plettenberg motor!! The more poles a motor has, the easier it is for a sensorless system to run them. The Novak motors are only 2 pole, wheras my Plettenberg is 4 pole. For some reason the U-Force hates the Novak motor. I haven't run any other 2 pole motors to compare, but I've heard the winding used is a big problem too. The ROAR and IFMAR rules allow sensorless esc's, but the motor specs will mean a sensorless esc is unlikely to run properly.