They've been around a long time. Mostly used by the amateur radio "multi-operator HF contesting" crowd, where you have a few radios set up all near each other in a room operating different bands in a competition setting, one 80 meters, one 40 meters, one 20 meters, one 10 meters, etc. Each operating position has a bandpass filter for the band to which the radio is tuned. Keeps the radios/antennas in close proximity from interfering with one another. But the bandpass filters can be useful when there is a lot of HF junk and you want to attenuate all out-of-band noise to maximize your in-band receiver sensitivity. If all you have between the antenna and your IF filter is the RF front end on a cheap CB radio, adding some external RF bandpass filtering can improve the receive capability.The filter is interesting and to be honest I have never seen one..
Link to HF contesting definition:
Contesting (a.k.a. Radiosport)