Duals are usually pistols, but can be SMGs as well. Their speciality is that the user uses two of the same weapon. Not all duals have same usage. BM9 and Judge pistols have long range and accuracy, because they are actualy Pistols, but still go in dual category because they are double. Sawed-Off are shortened shotguns and therefore are mostly effective on close range. Uzi and FMG9 are full auto guns, similar to Submachine Guns. This proves that each dual, like Experimentals, has different playstyle.
Dual weapon BM9 is default weapon for Gunlingers.
Duals are mostly offensive weapons. Gunslingers can be more powerful with Sniper rifles, but for the Ninja, duals are perfect for change of usually close range combat with shotguns.