hi pete i use the knauf cement boards,i find them much easier to cut than hardi
i use them on there own in wet areas and i rarely tank them,i have a sample of a peice of board which is set in a clear plastic framed water tank it has mosaics attached...also the adhesive lines are visible and also tile is grouted it has been in this box for years
it hasnt broken down,swelled..tiles havent come off,grout hasnt discoloured either
i agree its probably not as good as product as wedi etc but i find it affordable on my jobs and for domestic showers etc i am happy to install it as it is.
just my opinion