After buying cement boards for my shower walls (using a base for the shower ) I am having second thoughts about using cement boars after seeing how friable they are. Also after briefly looking at kerdi boards is seems easier to work with but I have the slight feeling that this is not for DIYers.
Also it might need more expensive accessories like screws, sealing paper or similar and I am not sure if the same water proof membrane (redguard) can be used for it or it needs some special for kerdi boards only membrane
Also it might need some special thinset
When it comes to price to cover a quarter of a 4x8 with kerdi seems to be double that the full sheet of cement board