I am a KR8 user, but have some 901 gear. I tried using the cartridges, but found them to be extremely tiny. My experience with the cartridges was like "tastes like burnt foam, tastes like burnt foam, that's nice, that's nice, that's nice, that's nice, tastes like burnt foam, time to refill". So it is relegated to dripping, which works just fine. I also like that the 901 atty works on my KR8 batteries and pass-thru. I can't see using it for an on-the-go device, but it is nice for testing flavors and when I want to have a few puffs of a "treat"
juice.
Note - make sure to keep the vent hole pointed up if you drip a 901.