With all of the people having issues with the center pin issue, I have an opinion and some advice.
Having owned an mvp, I had already gained experience with this issue. I never had problems with it, but as soon as I passed it on to my aunt, she quickly ran into the problem. I would just pry it up with a tiny flathead until it would make solid contact with her tank. But after about 6 months of her protank and evod leaking into the mvp, it finally decided to quit. I told her if she wants to use unsealed tanks, than she needs to be checking the contact on the battery every time she changes / adds juice, and to clean it with a qtip.
My advice is, don't use anything that is not sealed at the positive pin 510 connection on your tank / rda / rta, unless you want to deal with juice gathering inside your battery. Yes, the connection is somewhat sealed, but it is just poor practice and with the tanks out these days, there is no reason to not be using a sealed device. And if you are not rebuilding, than a Nautilus is the way to go with the iStick. Plain and simple. You don't need an adapter, zero juice can leak from the 510 connection, and when tightly screwed down to the bare iStick, it seats perfectly and produces a fantastic vape.
That said, I primarily use a mech mod with my drippers simply because I like to tinker, and I love to chase flavor. But, when I am on the go I will pick up my iStick with my Nautilus and know that I will be more than satisfied. I really think the iStick was a match made in heaven for the nautilus and a bvc head. The mini nautilus is even better imo.
So those that are having issues. The solution is simple. Use a regular or mini nautilus. Screw it all the way down, even snug it up tight if you want. I promise it won't budge that positive pin on your iStick. And it won't ever leak. Plus you get great performance and flavor. Stop mucking around with all these other off brand tanks, or even Kanger stuff for that fact.
I have been using my Magma with a dual 26g micro build at 1.1 ohm on my iStick. Sitting at 19 watts, it is really fantastic.