With my experience in the United States, I decided to develop my own solid brass resonators and to register them.
For acoustic logic. Your saxophone is made of brass, the resonator comes to "fill" the hole left by the tone hole.
Your saxophone is sublimated: the sound is richer, the projection is improved.
Completely hand-made in the workshop, they are made on demand to adapt to each instrument and obtain the desired result by the saxophonist.
It should be noted that the resonators represent an investment but are reusable at each overhaul.