Needed two of these to allow a pair of monitors to sit closer to the wall (not best practice I know but the space was necessary!)
They fit 8mm 3-core beautifully with no modification required, and the screw connections and clamp inside seem robust.
The plastic housing is good, there is a small amount of flex in it but as it won't (shouldn't!) be supporting anything other than a length of wire this is fine for it's purpose.
The only point I would draw attention to is the screw hole that holds the cover in place is straight in line with the earth pin, so be sure to allow an extra 15mm-25mm on the earth wire to circumnavigate this!
I am happy with my purchase.