The Eggbutt cheek piece prevents pinching of the lips and gives a solid feel against the side of the face. It also prevents the bit being pulled through the mouth. The release is slower than the loose ring and also introduces light poll pressure.
The central barrel allows for a separation of reins aids, enabling a fine tuning of communication. The limited movement of the barrel allows the port to adjust to fit a wide range of mouth configurations. The adjustable port allows the horse to manoeuvre pressures between its tongue & bars.