Ak12 features a good stat and a good rpm, it fires 5.45x39 ammo, this mainly focus on before s7 (not on market) , ak12 was relased at s5 and avaliable during s5 and s6
As t4 faction ammo 5.45x39 was provided in s5, this made this gun a very good option , as its good stats and rpm and being "free"(a few every week) at that time