The SS190 ammunition weighs approximately half as much as standard 9mm or 5.56x45 mm ammunition, and has a smaller volume than either. This means you can effectively carry twice as much.
The recoil impulse of the SS190 round is 1/3 that of the 5.56x45 mm and 2/3 that of the 9mm. This translates to one being able to get second and third shots off quicker, or in the case of a full-automatic fire, being able to empty an entire magazine and keep your shots within a 9 inch circle at 50 feet.
The SS190 round transfers nearly all of its energy into its target, minimizing "over-penetration" and reducing the risk of causing negative collateral damage. This is significantly better than the 9 mm, which loses only 30% of its energy in the target, as well as frequent over-penetration.
The SS190 will penetrate a wide variety of body armor, whereas the 9mm will not. It comes close to the level of penetration offered by the 5.56x45 mm round. It will not, however, penetrate materials that the 5.56x45 mm round also cannot, like the 4" ceramic plates which cover the heart in Level III armor.
Due to its low profile and high muzzle velocity, the SS190 offers a nearly flat trajectory up to 200 meters. The L191 tracer round precisely matches the trajectory of the SS190.