From The TimeSplitters Wiki

The Monkey gun is the most powerful automatic in Timesplitters Future Perfect. It is unlocked when electro chimp challenge is beaten with a bronze 'trophy' or higher. The monkey gun fires a clip of 64 bullets in about 2 seconds making it the fastest firing weapon in the game. Each of these bullets deal massive damage with just one or two of them capable of killing a player. The monkey gun bears a resemblance to the Mag Charger, the only cosmetic difference being a monkey face on the screen they also reloaded in a similar fashion. A monkey gun must be reloaded after every time it is fired this causes it runs out of ammo very quickly(usually 2 to 3 shots.

Due to its vast stopping power it is often classed as a superweapon and its use is frowned upon in PvP games due to the lack of skill necessary to attain a kill.Of course its power comes in very useful in comp stomp games where you can rack up a large number of kills in a very short amount of time and overcome vast odds.