This is definitely a new design, so it is different from the existing iStick 100W. FWIW, I'm not sure that I really like the hidden fire button. Since it requires you squeezing the battery door (very similar to the Smok XCube 2) to trigger the mod, it will make it too easy to accidentally trigger the mod, although having a separate lock switch will help. With my XCube 2, I will accidentally fire the mod often just from holding the mod too tight in my hand or just trying to put it into my pocket.
Also, looking at the Heaven Gifts website (from what I can find, it seems that Heaven Gifts is the only seller that is advertising this new model mod),
100W Eleaf iStick TC Express Kit W/O Battery
They mention that the batteries are run in parallel, which means it doubles the battery capacity. Most other mods have the batteries in series, so it doubles the voltage. So if you are using two 3000 mah 18650 batteries, it means that you will be in fact have a battery capacity of 6000 mah. That should definitely last you several days between charging. Since the mod is capped at 100 watts, you really don't need the higher voltage made possible by wiring the batteries in series. In fact, this is the first regulated mod I've heard of where the two batteries are wired in parallel. And the webpage seems to imply that you can either run the mod on just one battery, or two to double the battery life). The eleaf website also confirms that you can operate it either with one battery at 75 watts or two batteries and get the full 100 watts.
I guess the whole eleaf/Joyetech connection explains why the SS mode is configured for SS 316 wire, since all of Joyetech's mods have SS temp control set up for 316 wire. Having an adjustable TCR will come in handy if you want to use TC mode with SS wire, but a different grade.
It has been a while since I've used an iStick. The iStick 50 was the first box mod that I ever purchased and that got me into "real" vaping. Although I never had any issues with it, I know that eleaf went through a string of bad publicity with the auto-firing issue.