Typically you want AC on the input or output and DC on the other. You can use that shield to produce AC by driving the outputs with PWM (it is intended for that). If there was a 3rd channel on the mega-moto, you could drive a 3-phase AC motor with it. If you put a transformer on it, you can connect it to the line and do DC->AC or AC->DC. Normally we want the DC voltage to be higher than the AC, so it's not the ideal shield for line connection - hence the transformer instead of simple inductors. And yes, the inductors add to the size, but if you are driving an inductive load like a motor, they are normally not needed.