This version has the same qualities as the Celestine Flute Rexonator Balance model (see features under CFR-04-B). The difference is that it has an integrated custom-made adapter so that it fits perfectly inside your Alto Flute. It also has the 4 options of tonal sound among the brightest to the darkest through the O-ring to be selected according to your preference. It requires the sending of measurements as explained in the diagram, for its manufacture. Transform your beautiful unique sound into a sublime one. You have to try it, you will love it!