AFAI understand their basic functionality is to extend the frequency range for those UV-K5 devices down to 18 MHz when used with a hacked firmware. At least for RX, everybody warns about not to use a modified device for sending out of band (2m/70cm).

But the green PCB includes a resistor (for replacing the “choke”?) and microscopic smd capacitors to replace on the radios main board to fix problems (idk which ones) with the radio. The big orange board also includes a second circuit which seems to be an amplifier to improve SSB volume. This is my interpretation of forum posts & product desctriptions I don’t understand completely - thus my original post, hoping to find somebody who’s savvy on this topic.