Plastic only, but seems to work OK so far

I was a bit surprised that it is made of a kind of soft plastic. I expected a metal piece. It has to hold a fairly heavy box in a frame that constantly shakes as the car moves.
Assembly requires cutting off the superfluous parts as this is made to fit several models. I would have expected a bracket ready-made.
And of durable metal.
Now I installed it and have to use it for a while to see how long it lasts.