Think of the voltage as how fast the car goes and the mah (milliamp hours) as how big the gas tank is.
Even though the VK and the S6 use the same voltage (4.2 - 3.7) you're going to get more time at the 4.2 voltage with the super6 because it has a larger capacity battery.
You'll also see an increased performance or vapor production because it can deliver a higher flow rate of electrons due to it's size (garden hose vs fire hose).
Depending on how heavy you or your GF vape, a 14500 in a S6 wil very likely last all day as opposed to chaging batteries every few hours.
You would need to get 14500 batteries like
these and a charger like
this in order to use the S6.
If you're running Cartomizers you should stay with a 4.2 - 3.7 volt device for a while.
The higher voltage devices have a tendency to burn out carts and regular attys for new users. There's a small learning curve associated with higher voltages and some people don't like it.
Don't throw confusion, failure and disappointment into a new gift.
Go to the higher voltages as an experiment. You can have both with the Super6.
If you wanted to get the Precise you'd need the same charger but 10440
Protected batteries in lieu of the 14500's.
Don't get unprotected 10440 batteries for the precise because they're too short.
Whatever "Super T" unit you decided to go with, you can be sure that the quality and performance will far outshine any generic or off the shelf device that you're currently using.
Also, don't look at the time frames posted and wait too long to order.
David runs a small shop and these units are hand made and hand polished.
I order my Super6 on Feb 10th and recieved a shipping notice this morning.
The Precise is a brand new line. I expect a full 4 - 6 weeks.
The are a lot of people that jumped on the pre-order as soon as the units were announced. I'm one of them. Even though it is a smaller battery it's the ubber compact size and total cool factor that's desirable.
Last but not least. If you and your GF vape, get one of each or a total of two of either.
If you get one for her, you'll want it. If you get one for yourself, she's going to take it away from you

I'd hate to see you break up over a PV.
Good luck with whatever you decide on.
There are other mods out there that have a much shorter wait time but, nothing that compares to the hand machined quality of Super T (my own personal opinion).
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