This is just an analog magnetic gradiometer. It most likely has two fluxgate magnetometer sensors separated by about a meter. This unit is almost identical to a Schonstedt GA-52 or a Subsurface locators. They all are in the $400-$700 range. They produce an audio tone that shifts away from a base tone when you go over a ferrous magnetic target that is above/below a threshold. The operator can turn the switch to control the sensitivity over five or six ranges. I use a Schonstedt when I am looking for survey markers or a buried wire. I wouldn't use it for treasure hunting.