I don't know what FSDO's jurisdiction you have been in, but STL doesn't allow DEs to administer exams to students at their school. I would imagine that Chicago will be following suit after the little issue they had with a certain well-known flight school there. Oh, and I got pink slipped on one of those rides with a DE, so they do fail you.

Why have I paid to take exams with a DE? Because the cost was less considering that I would have had to wait at least a month to take a check ride with someone from the FSDO. Scheduling the flight when I want saves quite a bit of money instead of renting a plane to keep fresh and ready.