But i heard they decrease range :o
They do, both on real guns and airsoft guns. By extending the barrel, it gives the round less time to fall of its trajectory, but this increases friction which decreases speed and distance. A real suppressor is designed to scatter/suppress sound and decrease muzzle flash, however. Airsoft suppressors are really just compensators, used to increase accuracy, and make you look cool. My P99 can't shoot straight for stuff. The suppressor looks awesome and makes it shoot straight.

Sorry for the "you will get for free" in the picture
I want that free :(
Also I have the same model of suppressor on that gun that looks like a SCAR/G3/M4.