'Bisaigue' [Biz eye gu] seems to turn up the most hits. I had a go on one last week. Not easy but its weight could make it a cool tool. I was told they were custom made according to the height of the owner.
Not sure where they cross over with a 'Twybil'. Think the twybil was a smaller more pick axe-like tool more for chopping out than for pairing.