From The TimeSplitters Wiki

The Sci-Fi handgun is easily the best pistol in the game. It can fire as quickly as you can pull the triger, has a reasonably large clip, is very accurate and has a high damage rating, and also a small zoom ability. This version is a vast improvement on the Sci-Fi pistol of TimeSplitters 2, which was generaly recived as a very poor weapon. This version has the ability to fire ordinary blue plasma round, which are high damaging, or to fire the traditional 'rebounding' rounds, which are green and slightly less powerfull. As always, care is advised whilst the rebound function is active, as shots fired at a wall right infront of you have an alarming tendancy to bounce back at you. The compusary 3-shot-burst has also been removed from this version, makeing it a much more user friendly weapon. It has a magazine capacity of 16 and a large amount of reserve ammo, making it a very usefull weapon in your arsenel.

Of course, two Sci-Fi handguns are better then one.

In arcade matches against non-computer opponents, there's a trick with the handgun (duel wielding for best measure) that lets you confuse your buddies, and allows you for a quick getaway within the confusion. This will only work in corridor spaces--the arcade level Bunker is a snap for this throughout the level. When an enemy is chasing you--knowing that you'll probably get hit a few times, turn around, flick the Reflective Bullet function on, and let loose in a spiral around you, aiming only at the walls, floor and ceiling. The sharper the angle that you shoot it off at, the more that this "Bullet Wall" will be concentrated. Your pursuer will probably try to dodge the best he can--and eventually, start to back off from the flood--or just flat out panic. His vision of you will also be obscured, giving you the few short seconds you need to escape. Not reccomended to try multiple times in a row..people learn faster than bots.