These are commonly used by brass players to practice and perfect proper embouchure. Usually an actual mouth piece is cut to create what you see here.
The idea is that you can see if you have the correct placement of you lips on the mouth piece. Then when placed in the instrument you can practice blowing straight ahead. When attached to the instrument you can hear if the air is being forced into the instrument or escaping through the openings of the mouth piece.
This is for a Bach trumpet, but may fit others too.
I printed this with 3 shells and 50% infill on a Makergear M2. The mouthpiece came out very nice with minimal sagging or loose strands in the transition area to the tube.
The mouthpiece is very rigid and sturdy an I think will last a good while without breaking.