I have two of the Subtank Plus and love them. Great flavor and plenty of vapor to meet my desires. I highly recommend them. The organic cotton coils seem to last forever, for me anyway. I used the same one on my ADV for about five weeks before I needed to change it. I have yet to try the rebuildable deck, though, since I've never done any building on anything. I'm not certain of the exact dimensions if the iStick 40TC, but the edges of the Subtank hang over just a bit on my iStick 50W. Not enough to be unattractive (though I don't really care about that facet). The 7ml capacity is great for me since I go through a lot of juice in a day. Be advised that the Subtank with the .5 ohm coil eats a lot of juice, though. Let us know what you decide!