Hmm, yes, we have here various opinions.
Personally, I think that FF isn't good for Tremulous. In Counter-Strike for example, there are good reasons for it: 1) realism 2) gameplay element (not to shoot everything that moves)
But for Trem, these elements aren't in use. You see, Trem doesn't want to be (and isn't) a realistic game (lasers, Aliens and so on). Nor has it the same gameplay elements (many of you don't think about this one).
In Trem, there is a lot more responsibility when dying: You help the enemy team win easier, by helping them to advance to the next Stage, or by supporting the enemy with credits (because you die).
So, if a teammate shoots you, and then you die from a scratch, it causes a bigger problem than in any other game.
Also, FF isn't fair or balanced because of the models: While in Counter-Strike or other FPS games the models are nearly same the size, in Trem the Aliens are smaller than their Human counterparts (except for Tyrants). So it's harder to hit an Alien as an Alien, then to hit another Human player as a Human. Also, consider that Aliens have almost only melee attacks, but Humans can use splash damage weapons (e.g. Flame Thrower, which harms the wielder as well, when not skilled enough) or ranged weaponry, with slow projectiles (Pulse Rifle).
Conclusion: FF is really bad, because it can't be balanced in Trem.