The multi chamber ocarina adds aditional range to an instrument that by its design (Helmholz resonator) can not overblow.
By adding one, 2 or even 3 chambers, it makes it possible to play easily on one and half octave (from B to A) or more than two octaves (from B to D).
Playing 2 voices together, like double strings on violin is also interesting with multi chambers.
The major problem is passing easily from one chamber to the other keeping a good balance in the sound.
That’s why I use the Giorgio Pacchioni system, more intuitive and friendly in my opinion