"I have had the pleasure of fitting these for a customer. The faceplates are very thin and flimsy, they can bow out just from the pressure of the cables, and the plastic surround which grips the metal face can pop off with anything but the lightest handling.
These FCU's have screw terminals facing four directions: Diagonally down, diagonally up, straight up, and straight out the back. Try manouvering the screwdriver round that lot when the cables are a little short. Basically poorly designed IMO."