From The TimeSplitters Wiki

The electrotool is the 'lighting gun' of the timesplitters games.Primary fires a continuous narrow beam of electricity over long distances, while secrondary fire fires invidual more power bolts of electricity.

Due to its electric nature, it naturaly does more damage against robotic charicters and slightly less against biological characters.

The electrotool is generaly a poor choice for multiplayr matches, as it takes some time to defeat any enemies, usualy long enough for the target to deal much damage to you.
In story mode however it becomes much more effective espically on the robot factory level,as it is able to disable robots for a short time as well as overload shields on shielded robots it is also the only weapon that can destroy the power nodes.