> On the down side they also help the extroverts and the confident, and you have to be careful about preventing a bias towards those.

This is true, but it is also why it is important to get an actual expert to proctor the exam. Having confidence is good and should be a plus, but if you are confident about a point that the examiner knows is completely incorrect, you may possibly put yourself in an inescapable hole, as it will be very difficult to ascertain that you actually know the other parts you were confident (much less unconfident) in.