How much have you got to do? And are you going to paint or render the Blueboard afterwards?
I only had a 7 meter wall area to do so just used a bag of BlueBoard Jointing compound from Bunnings. It is pricey - $50 or thereabouts for a 20kg bag from memory.
From previous experience the joints stand out like the proverbial when they dry and are difficult to feather in to a later render or textured finish. To overcome this I taped them and used the joint compound to fill the joints and smeared it on as a thin render all at the same time. As it is all in one application the joint is not discernable.
If it's worth doing, it's worth overdoing