OK, you can't go far wrong with Rotring equipment. It is expensive but you are buying quality manufacturing. As a designer, I use this kit a lot and although most of it is very reliable and I wouldn't be without it, these compasses are frustrating to say the least. The pin is not sharp enough to anchor the compasses sufficiently and the resistance of the top hinge is too low. The result is that the compass either skids off the centre point or they start to splay out with very little pressure. Put sufficient pressure on the point to avoid the first, then the hinge in the arm bends breaking your lead or worse the nib of your pen.
I recommend avoiding these if you can and pay that little bit more and get yourself a pair of spring bow compasses instead.