It's four pieces of chipboard with a rack rail attached. Sadly these aren't captive nuts, so you will need 10-32 rack screws, but 5mm rack screws will also work. Other than that the rack rail is good.
The chipboard is garbage though. As a tip, leave the screws slightly loose until you fit all the gear in, then tighten. Otherwise the pieces won't sit straight.
It's really not very good, doesn't seem the slightest bit durable, but at least it's cheap and won't take up much space.