10it locks you in place
Every other hook drags you toward the block and then hands you back to physics. This one stops you dead the instant it grabs and holds you there, with gravity, momentum and knockback all suspended. You then drive yourself along the line with the movement keys, in or out, at whatever pace you want.
the best building tool in the game
The reach beats anything else, and because you can hang motionless anywhere along the line you can lay blocks at a fixed height across a wide gap without a platform under you. Firing the second hook while attached lets you leapfrog: you stay pinned to the first until the second lands, so there is never a moment where you fall.
why it is worse in a fight
Stopping dead is the last thing you want mid boss. There is no swing, no momentum carried into the next dodge, and the controls read oddly relative to the rope, since pushing sideways while hanging directly under the anchor does nothing at all. Keep a normal hook for combat and swap this in for construction.
cost
The Steampunker stocks it, which means it is available after a single mechanical boss, much earlier than its rarity color suggests. It is a painful amount of money at that stage of a run and still worth saving for if you build.