That is not great was already clear to me, but ...

... The arm is really not great. He is shaky, was in the delivery already chipped (paint was from), and is especially really small.
The recording at the terminal appears to be a bad design, there in the pen a slot in the locking screw is probably the inside, however, this does not fit. Therefore, the arm is seated in the terminal really not particularly strong and you can attach the arm virtually only with great difficulty in a position. In the leadership turn-existent. Long story short, you can work with it, but only if the arm can remain fixed in position.
Also, one should note that if you attached the arm on a table edge, you only 50cm with it comes away from the edge, since the arm is like saying quite small ...