Fogger is a great piece of kit, an original rebuildable tank atomizer made and designed by a Chinese company (Yiloong). It's like a combination of all the other RBAs in one.
I find that the air draw on the Kayfun is very tight, whereas on the Fogger v4 it is much more airier due to the larger air hole and the fact that it has TWO air holes not one. If you want a tighter draw with your Fogger, you can always adjust the air flow control to make the smaller too. With the Kayfun you're stuck with a tight draw that cant get any bigger or smaller as there's no adjustment.
Also... Kayfun tanks crack, I'm on my 3rd tank now
The Fogger tank is glass, so you're not gonna run into that problem with it.