Flint is a warhammer-type meleeweapon, which sends out a flaming trail that ignores shields and deals a critical hit to enemies in melee range when charged.
Parrying with the Rampart allows to safely charge up the flint.
The shockwave produced by this weapon's charged attack is considered a ranged attack and is therefore affected by ranged mutations such as Point Blank.
This weapon appears to be one of Concierge's detached hands stuck on a shaft, thus the flavor text "give an extra hand", and it mimics his ability to launch a flaming trail at the player.