From The TimeSplitters Wiki

The flare gun is a very powerful weapon in the hands of a skillfull player. For those less practaced, it is ill advised unless used as a last ditch effort. The flair gun has a very high damage ability, similar to that of a rocket, (and can kill the player too at close range) but are only one shot per clip and a long reload time, and the maximum ammo that you can carry is limited to 10 aditional shots. The flairs are inacurate, as the projectile travels in a spiral, and move slowly enough to be dodged at any range. However a direct hit is usualy enough to kill a player outright. Occasionaly they set a player's corpse on fire too. If you fire at a spawning player, the temporary invincibility will prevent him from dying, but it will set him on fire.

As with all weapons with the ability, two is better then one, as you can fire the other as the first is reloading.

Ps.one flare gun has more accuracy than two