While most snaffles have a single joint in the center, there are some that have more than one joint. Collectively, they are known as the multi-jointed snaffles.
This particular bit has a Dr. Bristol mouthpiece. The Dr. Bristol bit has a flat link in the center of the mouthpiece which lays at an angle to the bit, unlike to the French Link in which the link is at the same angle as the rest of the mouthpiece.
Like the French link, the Dr. Bristol doesn't have the nutcracker action of the single-jointed snaffle. Instead, the mouthpiece lays across the tongue and, when the bit is at a certain angle in the horses mouth, the edge of the middle link will be in contact with the tongue.
Multi-jointed bits have more mobility within the mouthpiece than single jointed bits, and so, some horses that may get "set" in a single jointed or mullen-mouthed bit, may go lighter and lean on the bit less in the Dr. Bristol.