I know its creator, Hans Kuijt, and I have seen and heard him playing with the " le freq" , I even know the previous version which he developed together with Ton Kooiman.
Hans Kuijt is a great player and educator and always very busy in promoting himself and his initiatives.
I am convinced that Hans truly believes in this thing. I am not convinced at all it does anything either in this present form or the previous incarnation (which was a piece of metal incorporated in the cork to , supposedly, aid the mouthpiece vibration being transferred to the horn)
Here what I already wrote before about it
............Anyway, not so long ago, a friend of mine Hans Kuijt ( a great player and educator no question about that!) invented an new gizmo, " le freque" which supposedly should help communicating the vibration trough the parts of a saxophone or other wind instruments which supposedly reduce the vibrations.
Anyway upon demonstration and at a 1 meter distance I couldn't hear any difference in the playing while he was demonstrating the influence of the " le freque" . Obviously I believe that Hans is honest about it and truly believes that the gizmo works. I couldn't hear it.
Whatever vibrations are in the wall of any saxophone these are of a minimal amplitude in relation to the vibration of the air column, besides the whole body of the saxophone has holes and cork and felt everywhere which would dampen and diffuse wall vibration to a level that no piece of ay metal could conduce even if the saxophone would be designed to work like a bell (which obviously isn't).
Of course one can, even in all honesty, believe this is the next best thing after bread and butter but before any commercial enterprise is started it would have been better to put this through SERIOUS triple blind scientific trials because, as it is, anybody can fool himself with the equivalent of the P-ligging (search button please!).
Another such fantasy device is the sound expander by Schucht
which should be the ideal companion to " le freque" by carrying the vibration of the upper and medium part of the saxophone to the bell..........another useless piece of expensive kit to do something that at best (but I doubt) is measurable in minute energy transfer and no influence on the sound whatsoever.
There are all sorts of these fantasies in the world of saxophone (and flutes!) banking of the insecurity and gullibility of people who have more money than judgement, all of these present " common sense " explanations based on intuition but no science, as I often say intuition is what makes us say that the sun sets while the horizon goes up, it is just not the way to face these things.