It’s better to buy the MP9 in CS2 when the Counter-Terrorist team goes for an anti-eco round. The SMG is quite effective against unarmored opponents, thanks to its high rate of fire and good accuracy even during movement. But penetration and damage with the MP9 is too low to deal with armor. Ambushes and swift offensive actions are the best with this weapon. The MP9 is also pretty cheap in Counter-Strike 2.