In reply to Dane1:
Quite aside from the rope catching, the knob would make a fair mess of you should you catch it on the way down.
Not a problem for me though as most of my screws (DMM and BD) are wound in with a DIY wire winder (similar to the Petzl Charlet one) - easy for the leader with a full fist rather than a finger tip grip, but not so good for the second.