The FMG9is a backup weapon that, while lacks a decent range and accuracy, is a good choice for players that require a good short ranged weapon (possibly to counteract a slow primary, such as the Intervention or the Judgement). It is usable by all classes.
The FMG9 is possibly the most powerful Dual in the game. It has high damage for automatics, and the second highest fire rate of all duals as well. However, you must watch you ammo count, as it'll be draining quickly; common of automatics.