I have always thought it would be useful, at least for the learning experience, to have and use a clear plastic mouthpiece. If for nothing else it would make a great embouchure visualizer.

Kelly Mouthpieces now have back in production several of the 'crystal clear' mps for tuba.

http://www.kellymouthpieces.com

I picked up the 18 for Tuba. Based on the Bach 18. That was my first mp 54 years ago, and I have enjoyed revisiting it occasionally. It is like an old friend.

For me, it seemed very satisfactory and I found the Lexan extremely comfortable on the chops. I normally prefer stainless and also have several Delrin models that I enjoy when I need to be getting a little more of a lighter and transparent sound.

I might add that I was always skeptical of the plastic/Lexan mps, essentially since they are marketed with all of those 'crazy' colors, and seem to appeal mostly to younger HS players. Now, having given them a trial, I find them a fine product in their own right. The are however different from metal products. My prejudice is history.

Being able to practice with it in front of mirror has made is easy to detect certain little 'quirks and foibles' that can be rather easily improved.

Earlier I posted my comments on 'upstream' vs 'downstream' embouchures. I always found that for some reason I unknowingly used both, that being an 'upstream' in the low register. There was then a break when I would adjust to the 'upstream' as I ascended. (much the same that singers experience as they ascend or descend over their voice range.) By being able to visualize the whole process when actually playing, and seeing what is happening, it then was very simple to make corrective adjustments simply by visualization. Changing old habits is not easy. So a short session on the clear mp and a mirror has become part of each day's warmup.

Plans are to grab one of these puppies for euphonium as well.

I really do not feel that is that necessary that it be a plastic twin to my 'everyday' mp. For 15 minutes as a visualizer it fills the bill. (It is nominally the same as what I use in metal.) But, I do like it for special circumstances as it does lighten the sound on my huge 6/4 CC, which can get overwhelming at times. Plus it functions just fine on the F tuba and the cimbasso.