IMO, FF makes the game less balanced. Aliens are typically played by more experienced players who are less impacted by FF, added to the fact that aliens in general are less impacted by FF (unless dretch FF is on.) If someone on an alien team is TKing alot you can just stay away from them. Little to no worries that someone on the other side of the room is going to try to shoot through you or take potshots at you for fun.
On the human side are less experienced players who are generally more likely to try to shoot through ANYTHING to hit that tyrant, especially when they learn that just hitting the tyrant can get them cooler guns if the tyrant dies!

They are also more likely to be momentarily freaked out by the swarm of wallwalking dretches spiraling in towards them (a particularly dreadful feeling when you just made enough for larmor and a helmet.) Humans already start at a deficit in that they usually require tight teamwork to win and are populated at least partly with members who are new and don't understand the strategy of the game, or care to play "as a team".
Except in 2v2 to 5v5 games, losing a large alien to TK almost doesn't even bother me. I can dretch out the evols pretty quickly. I usually don't evolve till I have points to do it twice when in large games. That way I can defend base if there is a push and I am killed.
Of course, with FF on as an alien it means that few humans get fully out of base without taking some damage so aliens get an even larger advantage there.
One of my favorite techniques is to jump through the middle of a bunch of humans, giving head shots. They spin around trying to shoot me and TK each other. I still get the evol though, cause I did the most damage

The side benefit is that the human team is less trustful of traveling outside of base together, and they can even get mad at each other for the TK! I on the other hand, I go goon

FF is horribly unfair to humans. Experienced players like it cause then they don't have to deal with spammed doorways IMO (a sure sign that aliens have camped a team of newb humans in.) I can't help but wonder if it helps the more experienced of us that likes playing humans look better, I must admit. Knowing how to fight the aliens 1 on 1 wouldn't look so dramatically good if newb teams could get kills without slaughtering each other.
edit: I mostly mean to say that humans are negatively impacted NOT in the TKs, but in the loss of health. A naked human that takes a small bit of FF damage leaving base is a one shot kill for a dretch instead of requiring a minimum of 2 hits. Thats one kill closer to s3 for the aliens, which almost always means the end of the game for humans.