That is correct, JustJulie. The cartomizers will actually fit directly on the 901 tip, but there's no airflow so only cartos that have a built-in airhole like the 901 atty will work unless you get the cartomizer adapter. I got it a few days ago, and I'm loving the GreenCig cartos and looking forward to trying some KR8's.
5V/6V can be a little too high on cartos on freshly charged batteries. I believe the cartomizers use a single wire coil heating element compared to the 3 piece atomizers that have a wire mesh element. Once my Xhaler's batteries have been used a little bit, the carto starts to taste a little better, IMO.