It's a ring that you slip over the mouthpiece and reed. It's not a new idea. I had one several years ago made by Pomarico for their crystal clarinet mouthpieces. This one had a screw adjustment so that it could be placed in different positions on the mouthpiece. I don't think the Bois has any adjustment mechanism. I never felt secure using a single ring to hold the reed on the mouthpiece.
I have one that happens to perfectly fit my Ponzol M2 stainless tenor mouthpiece. It works pretty well. I'd say you discovered the weakness of the design- you have to find one that fits in the right spot over the reed- not too far down or not too close to the tip of the mouthpiece.
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