Got my Kayfun 4 today. I don't know if it's authentic or not. I found a list of clues indicating fakeness on Reddit, and mine meets none of them except that the logo isn't centered between two air holes. I don't know. Maybe it's the real thing, maybe not.
The seller also included a couple of spare drip tips, one stainless and one glass (I've never tried a glass one before) and a gold Vicious Ant Kraken. That certainly appears to be authentic, which gives me hope that the Kayfun is as well.
The Kraken is a completely different build from what I'm used to. Stainless steel wick! Vertical coil(s)! I wonder how I'll take to them. Got to work on loosening things up a bit before I do anything, though: I can't adjust the airflow as of now.