There are loads of videos on youtube about kayfun coils. I use a 1.5 ohm single micro coil on mine with the istick. Great flavor and decent vapor.
Are you buying a original or a clone? I bought a clone on ebay that performs well and has the airflow screw (which I just remove) on the side instead of the bottom. I think it was $27. The performance is good enough that I am looking to buy genuine.
I am a mouth to lung vaper and the kayfun is the perfect draw for me. I have a subtank also and even on the smallest hole its too big for anything but lung hits in my opinion.