As CG said, a dirt cheap one-man crisis team is great for late game objective grabs. The actual damage it does is minimal and more of a nice bonus.
That said, a three man team with double flamers? That can do some damage. Mathematically speaking it's going to kill as many marines as you can fit under the templates, which holds up in play, and anything less durable than marines is going to simply evaporate. Be sure to have a couple of gun drones so that the flamers can spill over to the rest of the unit.
My troops setup tends to be:
- 1x 3-man team with flamers
- 1x 3-man team with plasma
- 1x 2-man team with fusion
- 2x 2-man team with missiles
- 1x fire warrior team