I have 2 and I love them BUT they are only for certain purposes. They have "low" mah (battery life) - the low is in quotations because a little over a year ago 1000 was more than plenty for many people. It is variable voltage, but only goes up to 10 watts. I would not use any coil or build below a 1.8 ohm because it will be hard to get a lot of vape off of it. It can NOT sub-ohm, so none of the new tanks like the subtank, atlantis, melo, arctic, etc. can work on it (nor does it have enough power to really fire them).
I think of the istick mini as a perfect start up battery for someone who doesn't necessarily wants to stick with ego styled batteries, evods or c4s.
Good luck on your vaping journey. Enjoy.