The BaGua BigKnife is exactly that. In terms of Chinese culture, practitioner a blade that has 2 edges – regardless of It’s size – is always referred to as a ‘sword’ (yes, bronchi because of language double-edged daggers are a whole other discussion). And, contrariwise, a blade that has 1 edge regardless of It’s size is always referred to as a ‘knife’.
The DaDao offers a tremendous amount of Leverage.  That much weight behind a sharp blade, with the versatility that it’s design offers in combat (particularly with a single opponent) makes for a very formidable weapon. The reach, the versatility of movement, are Far beyond the combative reach of the ‘regular’ Dao.

There is the misguided belief that the DaDao is only for training. The length and size of the DaDao, with all of it’s manipulations, are also a psychological intimidation, and on the field of battle the only thing that beats superior skill is superior mindset.
The Dao, like all weapons in Chinese Martial Arts, has a large variety of basic techniques. But Because of the extreme size and weight of the DaDao, there is a much larger variety of expressions available to each of those basic techniques.

Footwork and stepping become of paramount importance when using the DaDao against an opponent with a longer ranged weapon. Thankfully, footwork is the what BaGuaZhang is renown for, and versatility of stepping is it’s specialty.

In the conflict of Dao vs Jian, Which can prove Superior?  😉