Al in all the KT mini is a great tank. Even without the RBA coil head their still easy to rebuild.
I vape around 10ml a day and find that whatever I'm using, Atlantis (great), Arctic (great), but only for about 25ml of juice, then they all go down hill. So I just rebuild the coils and the vaping is back to great.
As for the vertical coils in the Atlantis and Arctic, the stock coils work great for the same 25ml of juice, and then go down hill.
I haven't found the right technique to rebuild these vertical coils, ( they never work as good as the stock coil )
BUT,,, that don't stop me from converting them to a horizontal coil.
The Arctic is a bit tricky with banging the sleeve of the coil out, replacing side cotton with aluminum from a can, re-insert the sleeve, make a hole through both sides of the aluminum, then running a horizontal coil/wick.
This works very nicely. (what I'm vaping at this very moment, in a 5ml {tall} Arctic Tank.)
The bottom line. Your going to pay for coils unless you take up the hobby and art of building coils and wicking.
The art of re-building (to me, and each his own), is fun and satisfaction when you nailed how to re-build and get that nice vape, (Cloud and Flavor).
To All, Enjoy
VapeOn