Was the mechbox broken when you bought it?
Check out
www.mechbox.com. TONS of information regarding AEG mechboxes and diagrams to help you if you need it. As for the one you posted i dont know much about that brand, but i would personally recommend a G&P mechbox. I hear a lot of people love them and the quality is really good with the 8mm versions. But, do a quick search on here as well. Their is plently of information about the different mechboxes available if you are willing to do some reading.