This bit is designed to apply more pressure to the lips of the horse, which increases rider control. The copper mouth piece promotes salivation, which encourages the horse to relax.
The French link bit is more acceptable to horses with a low palate as it does not have the nutcracker action of the single jointed snaffle. The mouthpiece lays flat on the tongue and allows for more movement resulting in a lighter, offhand ride. The rein pressure is more evenly over the bars for a more independent control over the two sides of the mouth.