How to mount powerboards with strange holes?
Orienting the keyways in different directions makes it less likely that an accidental nudge in any direction will disengage all the keyways at once. 

The best way to find the proper screw locations for devices like these, and indeed for any keyway mounted devices, is to place a short screw in each keyway, pushed all the way into the narrow end of the slot, and then press or tap the device against the wall in the desired location. The sharp screw points will mark the wall, indicating the proper position for the pilot holes and mounting screws.