The best gun insurance is with BASC imo, it is primarily for shot gun and bullet rifle shooters but the airgun section is growing. Almost all farmers connected to shooting will know off the BASC its main points are 10 million public liability insurance but also the fact that the insurance covers you AND the farmer if the injured person trys to sue. The ones you mentioned are pushed by the airgun magazines and may be ok but I would stick with the established BASC.