Purchased in July 2025 from NachtmusiK BRASS FACTORY for 12,800 yen. This product is designed to be attached to the slide of a brass instrument to amplify its resonance and improve its response. It also helps with high notes and intonation. I used it for about a week, and it definitely changed the feel of playing! However, I stopped using it because I tried it right before a competition and the change in feel was too drastic, and also because I was using a mouthpiece ring. I've decided to sell it.