I have four "good" Kayfuns one 3.1 that works perfect, two Lite plus v2 and one Lite plus v2 twin airholes. They are my single coil faves. I don't count two junk $17 Kf31s that I've converted to permanent top filling by plugging the deck juice hole and drilling-threading the top cover.
For twin coils I also have a pair of Foggers 4; one of the second version (first with threaded AFC ring, small deck) and one of the big deck version, first iteration.
Those two are my preferred double coil vacuum tanks. Kayfuns work great between 1.2~1.6Ω. The Foggers are great for lower res values 0.8 to 1.2.
I have other two vacuum feed tanks are an Aga-T7 which is reat in many ways and very versatile but a <female dog> to build. It demands a very precise cross shaped coil/wick configuration of exacting length and thickness or it just doesn't work. Otherwise it's great. Even with the top cap fill hole it's a PITA to refill. You have to place it horizontal with the hole at 12 o'clock and the screw is a micro allen plug. heaven forbids I ever misplace that little Allen key 'cos I won't be able to fill it again,
The second of these, and last addition to the vacumm tank collection, is an Erlkönigin wich is -as you are aware- a superb piece of engineering and machining; just like a Swiss watch. It's also par with the Kfs in flavor but not very flexible on coil and wicking styles. Not that it matters as long as the functioning is excellent.
I've only used it once each with silica, ecowool and braided cotton wick. It works perfect with all of them but I keep returning to ordinary drugstore cotton sterile cotton. The tank holds a whooping 6 ml of juice and the wick lasts for three or four tanks. The coil I haven't changed since I hit its sweet spot at 1.0Ω.
