To add to Baditude, Genny style tanks are difficult to build properly. I had the Smok RSST as my first RBA and I hated it. After some time, YouTube videos, and a lot of patience I was able to get it to hit very well. That being said, it was nothing like an RDA.
I, personally, don't like the Kayfun. I've had 4 of them now, thinking that I might like it, and it disappoints me everytime. That is due purely to my wants and needs when it comes to an atty. So, what are you looking to get from your vape? Clouds, flavor, etc?