I use a couple of iStick 30's for when I'm out of the house, both with Kanger Subtank Mini's and .5 ohm coils and they work fantastic. Small and portable. I rarely go above 12 watts or so with the Sub Mini and I get more vapor than I've ever gotten on any device other than a dripper. Though I'm not going to win any cloud chasing contest, it is a very satisfying vape.
I have noticed that the Kanger tanks seem to be more efficient than the Atlantis, though. At the same wattage the Aspire tank just doesn't give as much flavor and vapor as the Kanger, so if I were getting an an iStick, and it was going to be my only mod, I'd get the 50 watt version - especially if using an Atlantis.