The mullen mouth is very stable in the horses mouth. It has a medium port creating space for the tongue and relieving pressure.

Stainless steel is the most common material for bits. Durable, easy to
clean, tasteless and it does not rust.
Blue sweet iron oxidizes easily to create warmth and a sweet taste which
helps with bit acceptance and encourages salivation. The addition of
Brass Alloy inserts where present, help produce a warm, more palatable
bit. Please note the blue color will fade with use.