The Dr Bristol is very similar to a French link as a Dr. Bristol also has a flat plate in the middle of the mouthpiece to reduce the nutcracker action on the horses tongue. With a Dr. Bristol, however, the flat plate sits at an angle to that it applies more pressure to the tongue than a French link.
The Dr Bristol works primarily on the tongue with a sharp action due to the straight edged angled plate. A strong bit not recommended for novice riders, but can be very useful on strong horses and those that lean.