This "corner" is made of plastic. An aluminum there are not (why not ?!)
The quality I think is not comparable with the aluminum cable channels from Hama. The lid shall be liable, but not as great as in the aluminum channels. Just when things get tight in the channel, the corner is too difficult to get.
Furthermore, plugs and screws that are (as well as the channel Alu) very very poor quality and should be replaced.