For use around a farm or as a truck gun for varmints, five- or ten-round mags make sense. All these 20s and 30s are for playing, not for serious use. Well, this side of a Rodney King riot, and we really don't have all that many of those. Nothing wrong with having them but don't take them seriously.
You're from BATFE? Come right in! I use all your fine products!