1. Yes.
2. Flamberg/rigadoon aren't worth it.
3. Mostly the same as other weapons... the first hit though, is the good one. Not using the 2nd and 3rd hit is beneficial often.
4. I usually rely on them for heart of ice. I use my snarble barb with undead high on it.
5. They look cool, especially rigadoon/flamberg. The snarble barb line doesn't match much though, and the other is boringish.
6. I actually prefer the flourish style of charges, because if I use it correctly, I can dodge stuff. The other line, the snarble barb, makes me stand still. This makes me prone to attack. Like spy said, it is good for trojans though. And beasts. Its good for those too, but they're easy anyway.

-I just use a Fearless Rigadoon because that's what I have.
-I hear that the other Flourishes are better, Flamberge would be nice for poking at a group of enemies with that higher proc...
-I focus on using first and final hits of combo unless an enemy is against an obstacle, in which case I spam 4 hit combos.
-Nope, could always bring a SSS, or WHB, or Triglav, etc.
-I like how my Fearless temporarily removes the aura effect on the SSS I have when switching weapons. The tracer is fun to spin 'round with.
-Flourish: more damage to a group of clustered enemies

Yes.
Flamberge is never worth it, Rigadoon is only worth it 1/100 times in PvP. Overall, not really, no.
Shield canceling in PvP with this weapon is essential, unless you use auto target. Even so, the third hit can and will leave you vulnerable for a long time. In PvE shield canceling isn't required against most monsters these weapons are viable against (everything but slime and construct), except fiends.
No, not really. They're definitely the easiest swords to get to a high effectiveness level in PvP, but other swords can be just as effective if you spend a little more time with them. In PvE they aren't that special, except, once again, against fiends. Their knockback on the first swing and vulnerability after the third, combined with their not-incredibly-amazing charge attacks makes other swords as good or better in certain situations.
BTB>FF.
BTB charge is better at AoE damage, safety, and (I think) single target damage if you manage to hit a single target with all the projectiles. The Flourish charge throws you right into the middle of the fray, with a long recovery time to deal with.

1.Do you use any of them (well duh)?
Answer:I have only used Flourish in missions with Fiends,I hate 'em.

2.Is it ever more worth it to use one over the others? Does the Flamberge or Rigadoon statuses ever justify the loss of power of the other two?
Answer: I think Flourish does a lot of damage and not in need to cause status effects on enemies.i prefer staying in Barbarous and Flourish side.

3.What strategies do you employ when using these weapons? DO you [need to] employ strategies when using these weapons?
Answer:I don't really use them,because of the push forward they do to you.Spikes are always there in every mission and deal a lot of damage.I don't use any strategy,I just go and rush.

4.Is there any time when you HAVE to have these weapons?
Answer: Question 1's answer. xD

5.What do you think of its looks?
Answer:Barb has got a better skin,but it seems like they deal the same damage.

6.Between the Flourish style and the Barb style, which is a more effective charge? Why?
Answer:I haven't really paid attention to their charges,but it seems like people like Barb more,cause of its look and charge attack.To me,they look the same.