The Loose Ring Tube cheekpieces lies flat against the horse's face giving a more solid feel against the side of the face, while preventing pinching of the lips and the bit being pulled through the mouth. The mouthpiece is quite fixed in the mouth and concentrates pressure on the bars but the loose rings allow for a quick release.
The Colin Miles is a great schooling bit with a 55mm centre piece creating greater tongue pressure and reducing bar pressure. The rings give the horse something to play with and help keep the horses attention on the bit.
This particular joint exerts more pressure than the Control Plate or Elliptical.