I looked at adding this to my former department’s front line engines to increase radio coverage at scenes, especially for inside building or below grade coverage. The newer models operate automatically- they can turn on when the vehicle parking brake is set for example- and simply act as a 10 watt portable repeater.
In our situation, the plan was to have a simplex 700mhz foreground channel which would feed through the apparatus radio to the county 800 trucked radio system. This meant the portable radio signal would only need to make it to the Engine instead of trying to hit the nearest radio tower.