Some will contain filters to help stop moisture , some work better than others , the Hills pumps contain a dri pack but how effective it is I've no idea , it looks like it filters the air as its going in , not once its been compressed , Andy had one and it was clearly rusty on the inside after a few uses. The FX one contains a magic Filter , they are basically glass balls that the condensation seems to stick to, I'm no sponsor of FX stuff but I do have one , mine actually has 2 of these magic filters inside it, they do a very good job of catching the moisture, but it's swings and roundabouts , the FX aren't designed to be serviced , the hills ones are , then again the FX and Hills are very expensive , Amazon had a session a while back , although they were all cheap Chinese offerings , they were doing them for about £6 delivered , they work absolutely fine and came with spares .
I always run a seperate inline filter on my hose as well , on the FX the cotton filter never even gets damp, so the magic filters must work quite well . But I'd recomend an inline filter whatever type you might purchase , as long as you take it easy, pump then stop and let things cooldown , then pump again, you'll fill a rifle no problem and won't die trying