The EEZYCUT Trilobite with Velcro Harness Pouch is a very popular line cutter with a harness pouch. The Z-Knife itself uses a double-edged razor, which is much sharper than a traditional dive knife, for a quick and clean cut. But the blades are shrouded for safety, so you only cut through what you want to.
The design of the Trilobyte allows you to cut through lines up to 12mm easily. By trapping the line under the shroud it presses the line against the blade. As you turn the line it slices through, making it thinner so it can pass further under the shroud and moving along the blade for an effortless cut.
When the blades dull, you can easily change the blades inside for readily available spares.