The Dee Ring is very similar in action to the Eggbutt, it will prevent pinching of the lips and gives a slightly more solid feel against the side of the face. It also prevents the bit being pulled through the mouth. The release is slower and some slight poll pressure is introduced.
The Mullen is a strong bit which creates direct pressure on the tongue. Used for a strong older horse and will also bring the head down.
The Round Twist creates more pressure points on the bars making it stronger than the Smooth Mullen.
Disclaimer: Sweet Iron will oxidize when it comes into contact with mositure, this oxidation process encourages salivation which improves acceptance of the bit. This process changes the blue colour of the Bomber bit to a brownish grey. If not used for a while, any build-up may be removed with a scourer and wiped with a damp cloth.