But still an important question!
As a fencer and collector of swords, i must ask... What could Kai Lengs sword possibly be made of? It can pierce through the metal of a car and it can slash at you, but it can't hold being backhand-slapped by an armored gauntlet?
This means: The sword is oddly 1-purposed and Kai Leng is one hell of a swordsman to be able to use it.
Unless he just channels his biotic powers into it. I guess that could work.