Schluter recommend 2kg m2 to fix mat and 2kg m2 to fill voids, I still use a plasterers float to lay, can get good pressure with this. generally dont fill voids first as good to use up rapid set thats going off to fill voids as your tiling
Most vinyl flooring / carpet wholesalers will stock these it's a vinyl floor and wall roller cost around £20. A lot less tiring than troweling the ditra/dural.
Got all the bits ready to make the Karl Dahm style upright roller now, will see how it performs. Should give good coverage with the bag of adhesive weighing the shaft down.