I use the Smoktech 3.5ml tank as well but on an E-Power. Crystal Clear Vaping has them too, but with free shipping so it ends up being cheaper than getting them from Madvapes and paying shipping.
I dont like dualcoils at lower voltages so instead of the dualcoil that comes with the tank, I use a 1.7ohm Ressurector in the tank and they work alot better. CCV sells prepunched Ressurectors too for a good price that have the metal base for the smoktech tanks, but you can just use a regular carto without the metal base too