I hate to put this page under this category. But I want this next to the Mazzeo entry.
Stubbins' register mechanism is perhaps the best attempt to improve the throat tone Bb— which is so notoriously thin sounding. See the resonance fingering page for how most players improve the A and Bb throat tones.
I am indebted to woodwind.org’s Ralph Katz for this great information:
I have reviewed only one Stubbins clarinet, a Vito. I would think that some professionals would want to have a clarinet for the times when the Stubbins mechanism would give a great advantage.