I know a few years back the Brocock & Webley stirrup pumps were badged FX made, & the instruction leaflet still said FX on it,

Most moisture is removed by condensation due to expansion cooling, which is why the vent is at the base & when you vent it, drops of water come out, (ps always leave the vent open after use)
generally the inline filters are for particulates not moisture.

The main differences are the number of stages, good ones now are 4 or 5 stage, and the basic build quality / parts availability.