From what I've seen, there are very few people who carry around the weapons I have mentioned. I've heard reasons such as how they're worthless in most circumstances. (Grinding Vanaduke? Use a Blitz Needle. Beasts and Fiends? Use Final Flourish/Dark Thorn Blade. Haze bomb? Use Shivermist/Voltaic Tempest.)
In my opinion, these weapons are pretty fun to use, and a person should disregard what other people say about your choice. This also applies to armors helms and shields.
What weapon/gear do you see the least/consider impractical?
Ash of Agni Underused? It's the Best DPS Haze Bomb.
The others you Listed, though, are Underused.
-VPB because it only Deals Normal Damage & the Fire is hard to Come By
-FF because it has Lowered Power for such a Small Chance of Causing Fire. The Enemy'll be Dead before you have a Chance to Inflict a Status.