The poison attack/defense debuff is fairly insignificant; its only use is to prevent healing. In this capacity it's utterly useless outside of arenas involving Gremlins or Wings. If your friends already have an Ash/Shiver combo going, then go ahead and use it. But otherwise even Voltaic Tempest will be better.

Not that Voltaic Tempest is bad but it combines damage and crowd control without matching up to either Ash or Shiver.

EDIT: Spine Cone is powerful against non-Slime/Construct enemies; it does the same damage as the Blast Bomb line against Gremlins/Undead and of course more against Beast/Fiend. The major difference is that it knocks enemies down without blasting them back. However since arenas tend to be full of Constructs you will likely never see it except in the hands of a pure bomber. AFAIK the 5* graphic doesn't do anything.

I used to have a Toxic Vaporizer, but that's only because I am new to the game and thought that poison takes away health. Right after I learned that poison only prevents healing and lowers attack and defense, I ditched it and changed to Freezing Vaporizer. But this doesn't mean that it doesn't have it's uses. In an arena or danger room, it will prevent healing which is extremely useful as those Menders just can't stop healing other mobs and each other. This is also a viable bomb when killing JK, you won't need to equip many vials (do equip some because there are loads of monsters there and can hit you, thus stopping you from charging).

I have a Twisted Spine Cone and I think it is great. It is the one of the three Piercing bombs and the only pure Piercing bomb. The other two is Radiant Sun Shards (Piercing and Elemental) and Ionized Salt Bomb (Normal and Piercing). People have always been talking about how Ionized Salt Bomb sucks so you should never ever lay your hands on one. So if you want a pure Piercing bomb (bad against Constructs and Slimes, good against Beasts and Fiends, ok against Undeads and Gremlins), get Twisted Spine Cone but if you want to mix Piercing and Elemental together so you don't have to carry so many weapons at once (bad against Gremlins, Constructs, Slimes and Beast, good against Fiends and Undeads), get Radiant Sun Shards.

Poison is the best stat in my option! I love it! You will deal 10% more dmg, the affected enemy deals 50% less damage and it will become minor damaged instead of healed. Guess about 1-10% of the heal turns into damage.
I got these infos from a supporter, just the numbers did i test by myself.