The reach and range for one. I'm sure a normal longsword would give you a similar reach but having a weapon like this allows you to switch sides very effectively even on the ground.

[She pauses a moment. Mentally she can visually the weapon in her hands given she's practice with it so much.]

You can pass it between your hands very easily so no matter where someone attacks from -- your right, your left, behind or in front -- you can move in that direction without wasting too much time switching hands.

[She moves through a practiced set routine. A pass over her shoulder with the downward slash before her, a pivot on her heel for an upper slash behind. The Mahne is always in motion, grips passing between her hands.]