IME, the WPC-Z wall mount system is not just an accessory but an essential building block to allow the Oyaide, or other outlets, to perform to their maximum potential and worth every penny for the ROI delivered.
An additional item I would like to mention is Oyaide is now offering an unplated version of the P004 male plug which should be a most synergistic match with the RO outlet.
As an aside, I just received an unplated P004 but have yet to press it into service. I'll report out when I have done so.