From The Heretic Knowledge Vault
Sara Amraphel uses one, and is proficient enough with it to decapitate a troll without too much difficulty. This was apparently inspired by the use of the same weapon by Anita, head of the Ensigerum, who's reputed to be one of the most skilled fighters ever in the order.
According to Sarine, the weapons were never meant for actual combat, simply "to look impressive and showy when swung around." This implies that their primary function was in the display aspect of dueling, or in other spectacles where the weapon was designed to be wielded without risk to the user, either by itself or against an opponent who knew what he or she was doing enough to not hit when not required.