Granma,
I've made one (obviously from the instructions I put on here about how to make one). And I've used it so far twice during investigations. If you ask me from a technical standpoint, I don't see how it can possibly work. It supposedly allows spirits to manipulate the frequencies to pull voices in and cause them to be heard at the appropriate time to create phrases or sentences. From a purely scientific point of view it sounds like nothing more than a glorified white noise generator, which we are then using to matrix the responses from to make them mean something.
Having said all that, I do have to say that he one time I used it during reported inhuman haunting, it did seem to give more results than simple coincidence could explain. So based on that I would have to say that perhaps there is something to it. I've learned that we can't always explain everything easily, it sometimes requires building blocks which we don't yet have knowledge of.
If you do decide to get it, yet the larger model (20-125) since the smaller one no longer is convertible to a ghost box. If you get one and need help converting it, let me know I can talk you through it.