As far as Kayfun the clones go, I have an EHpro 3.1, Hcigar 3.1, Tobeco Lite+ clone, and a Rocket.
The Rocket seeps juice if you lay it on the side, not bad but a bit, whistles the worse of the bunch, the build deck is pretty crappy as well, that said it vapes as well as any of them, I use it for Pluid, and other hard to remove flavors. don't really care for the plated brass, but no issues so far. Biggest annoyance with it is the top O-ring, it does not fit into the top section, and squeeze between the top of the chimney, and top as you screw it in, tends to pop out often. Easy fix is to to use the rubber from a protank head inverted.
EHPro 3.1 nicely made, threading is a little sharp, PITA to fill through the fill screw, seeps a little juice from the fill screw, and tank sections, very little, but still does it. very minor whistle, nice build quality on the deck.
HCigar 3.1 probably the best machining of the bunch, but suffers same seepage as EHPro, otherwise almost Identical flaws and performance.
Tobeco KFL+ This is easily my favorite, machining is sort of between the EHPro, and the Hcigar, Adjustable 510 pin, beveled fill hole with o-ring on the screw least whistle of the bunch, lightest, no leaks or seeps, I also bought the $4.99 clear tank from madvapes for this one. like the bottom fill much better then the 3.1 clones. I bought it from Ebay, so a little more then you could find it from China, hate to wait though. pretty much same thing as the guy selling the so-called Black Edition on Ebay.
Kayfun Lite Plus w SS Clear Tank Adjustable 510 Pin Bottom Airflow Fill Screw | eBay
I know it is cool to support the original designer and all, and I do like my real deal, and will buy a mini one of these days. Only thing is not everyone can afford them.
All of these give very close performance, the Rocket is good to try and see if you like the Kayfun, but it would be my last choice for sure. I really like the Tobeco but only with the recessed fill hole, and adjustable 510, I will be getting another when funds permit.
I run them all with microcoils about 1.2 ohms, and cotton, takes me about 30 seconds to change the cotton, coils usually last for quite a while. They are much less fiddly then the fogger, builds go faster, and the Fogger even working well is not hands down better. Airflow is adequate, I remove the adjuster screws in all, I like an Airy Draw, ran the Fogger wide open, the Kayfun clones are not all that much more restricted.
Pick one up you won't regret it.
EDIT: Forgot to mention unless your using high PG (thin) juice the rocket doesn't fill decent from the fill screw, that was the other big annoyance with it. If I'm using thicker juice, or just don't want to mess with the fill screws I usually unscrew the top section and fill with the tank open, this goes for all of 3.1 clones I've seen. And if you don't fill it properly it will flood badly when filling from the open top.
