Airflow control is a plus for me not so much the Pyrex glass tank though as I don't Vape heavy acid juices is it just the filling aspect that puts you off ? Thanks
The design problem for filling has been solved; the protanks, the aspires, and most of the tanks being used are now bottom coil; and refill is simple; just turn it over, unscrew the main tank piece and put it aside like in a cup; and you can them just top up the tank, or maybe you want to adjust the atomizer or check it or whatever.
With the kayfuns, if you turn it over, and attempt to unscrew the main outer piece from the atomizer, to separate it while the liquid is inside, the chimney becomes unsealed from the top drip tip area, and all your juice flows out.
I'm not saying it's a bad design per se, but given the wide assortment of tanks that don't have this problem, it's a big --- outdated design by todays standards.
By contrast look at the Taifun GT: You can take off the top with your expensive eliquid in it just like a protank type:
Also possible with the squape:
Same thing with the Rose :
Same with the expromizer: in fact it looks like a big protank:
But with the Kayfun:
You can't hold your eliquid in the top part shown on the left in the picture because it will all just drop out through the drip tip.