Hi,
The science behind this kind of device suggests that it is not a descaler, per se, but rather is an inhibitor, if it works that is. The science would probably have to be that of vibration, where it keeps the particles from interacting the way they normally do in a pipe type flow system where there is probably low turbulence, which brings us to another interesting idea (later).
It could work if done right because the stuff that travels through the pipe follows a certain kind of flow which is less toward the inside surface of the pipe and a sound wave could feasibly disrupt the regularized flow which could mean less gathering and less sticking.
A question that comes up is what is the best frequency, and what is the best or at least the minimum amplitude or power that needs to be fed to the pipe to inhibit the gathering and sticking?
Another question is will it work as well on horizontally mounted pipes as well as vertically mounted pipes?
It's hard to determine what the operating characteristics should be and how well it works in various applications.
For example, will it work in a small coffee pot like water heater of say 1 or 2 quarts capacity? This might not be too hard to test, but using devices made from different manufacturers would probably lead to different results.
Just to note, i've seen scaling 1/4 inch thick on the side walls of a pipe in an old house that was only about 5/8 inch inside diameter anyway, so the water flow was extremely restricted.
The solution might be to use a spread spectrum, but then the power for each frequency will be reduced, so the problem of how much power is required comes up again, and how much is this going to cost over the year? My guess is that it would have to use a lot of power to be effective over the whole length of the pipe, so it would cost quite a bit to operate.