The Williams cheek piece allows for multiple rein positions. If connected to the main ring the bit acts as a loose ring, but when connected to the bottom ring it promotes pole flexion by creating more positive poll pressure. The Williams cheek piece helps to prevent drifting.
The Barrie Reversible is a severe bit due to the center links of the two pieces being offset by 20mm giving it a double nutcracker action, which creates more tongue and bar pressure.
It is a versatile bit that can be flipped and used either way. The Round Twist providing a harder bit and the Smooth creating a more forgiving and softer bit.
Great bit for the experienced rider and strong older horses.