The C-9 Comp is the larger version of Hi-Points 9mm handgun, one major difference from the C-9 or C-9 Compact, is that it is "Compensated", meaning it has a specially designed "compensator" attached to the end of the barrel.
The compensator works by forcing some of the hot gases, escaping behind the bullet, to go upward through specially drilled holes in the top of the compensator. The escaping gases push the end of the gun downward; helping to eliminate some of the upward motion caused by the natural recoil of the gun. The Compensator has also been machined on the underside to accept laser sights, or "tactical lights" for better target identification in a self defense, or tactical situation.
Another difference between the C-9 and C-9 Comp. is the barrel length. Its 4" barrel is 1/2" longer than its sister weapon's providing for better accuracy and balance. The compensator and extra bulk push it up on the scales a bit as well. Weighing in at 35 oz., it is fully 10 oz. heavier than the new model, and 6 oz. heavier than the older model of the C-9 Compact.