Several years ago I bought this kit but only got around to building it last week. The manufacturer calls it an antenna tuner but I insist upon referring to it and other such devices as an antenna coupler because it doesn't actually tune an antenna. Aerials can be tuned by changing the sizes of their elements or the values of their lumped reactances but this device is not part of any antenna. It's function is to couple a feedline to an aerial so that energy can be transferred from one to the other. I am also willing to call it a transmatch because it does its job by transforming or matching impedances.
The ZM-2 is a nice little unit that if very easy to adjust without the need for an external SWR meter. The empty holes in the corners are for screws that I still have to buy to hold the faceplate to the plastic box.