The only time I had to use the brace position was on a Northwest DC9. We had circled over Detroit for over an hour whilst the flight crew tried to find a solution to a potentially serious problem and the cabin crew briefed us on what to do.
I remember being alarmed by the tray table stow/secure clip. I imagined that if my head struck it with force that doing so could seriously damage my skull. Shouldn't these be flush and not protrude?