I've progressed all the way up the ranks in peripherals, from a membrane keyboard in my laptop along with a tiny ass wired mouse, to a cheap Cherry MX Red keyboard and wireless Logitech mouse that was really ergonomic, to now a K70 RGB with Cherry MX Browns and a Func MS-3 R2 which is eve more ergonomic with more buttons and a better texture to it.
It's not a necessity, and won't boost your K/D by anything dramatic, but there will be those times where it will be the reason as to why you win a gun fight, or just makes it that much easier to play a game because of the extra buttons, variable DPI, macros and keyswitches.