Mullen mouthpiece has a very gentle action.
This is the only common snaffle bit that does not have any joint at all. With its slight curve, it is often considered to be a mild bit because it puts more pressure across the tongue instead of the more sensitive bars. However, for that reason it is not typically a bit that will aid in the lateral flexion of a horse’s head. Hence it is not often used in dressage, but more often as a pleasure riding bit on sensitive mouthed horses.
Because it lacks a joint, there is no possible nutcracker or pinching effect in the mouth, which also makes it milder and can be advantageous for horses with sensitive palates.