Zenon,
The wax guards are simply to protect wax from entering the receiver and blocking the tubes, which can cause weakened sound, or if completely blocked, can cause an aid to sound “dead”. We do recommend that they be changed about once every three months, sooner if needed, but if you never even get wax on your domes, your ear just may not produce much wax. It will not hurt anything to change them out every three months, but if you notice they still look clean (look at them from the back and see if you can see through the many holes), then you can bump it up to every six months or so. As far as I know, they don’t have a moisture filter, but as long as you have a dri-aid kit that you use at night time, then you should be fine. Hope this helps!