For BLU this item has two uses:
1)wearing this item allows the player to stack major stat+ gear when using Pinecone Bomb for some pretty good damage
2) Arguably the best BLU nuking spell "Eyes on Me" has a large CHR mod, so using this in a macro provides a very good bonus in an otherwise meh equip slot.
Leviat: Ranged Accuracy does not affect Mistral Axe whatsoever. Yes, the WS can be used from a distance, but it is still considered a melee attack, not a ranged attack (as evidenced by the fact that it stacks with Sneak Attack and Trick Attack).