Looks like it's using relays to switch the output between the different extruders. The risk is that the relays might be switched when the motors are powered, which is bad for the stepper driver and the relay contacts. Presumably the firmware that is intended to be used with this board turns the stepper driver off before switching the relays over.
I think this is a poor approach, and of course it's no good for mixing extruders such as the Diamond. I recommend using a separate stepper driver per extruder.
Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]