The broad machete has a unique world model and an appearance that sets it apart from other machetes; the bolo-style blade is well-traveled and well-honed, making it a more conventional machete as opposed to the makeshift design used by the Legionaries. It also has a unique Pip-Boy icon when selected.
The broad machete has considerably higher DPS (especially at higher levels), and a higher base damage as well. While it does not take advantage of extra limb damage like other machetes, it only weight 1 lb. These factors make it an excellent weapon for melee-based characters, especially early on, where the broad machete tends to outperform other melee weapons by a considerable factor. It's forward power attack is more akin to non-player character power attacks, as well.
Unlike the normal one handed melee weapons, it does not have the "Back Slash" special attack.