to be clear, it is basically used as leverage when you are tightening your needles. the only time my needles have come loose is when i haven't used that key thingy.
i have heard some people have had luck loosening that join up by kind of bending it back and forth. i have also heard others have broken it by trying that. essentially, that is how almost all boye circs are created so they are meant to be that way.