The problem may be the juices. It was giving off this awful burning taste, even after changing the atty head, cleaning, etc. Apparently, according to the people of YouTube, these don't really like VG. And I've been doing a lot of VG lately. What I did was I now only fill the tank about half way, and give it a flick every few pulls to pop bubbles and loosen the vacuum. Seems to have fixed the problem. Next order I'll probably ask for PG - or mostly PG - instead to fix the issue. But I'll probably switch over fairly soon and use this as a backup system. I've been using mine about 2 months now, maybe not that long.
I've only had one pure VG juice in mine, and I honestly don't remember if I had any issues, that was awhile ago. I mostly do 50/50 or 40/60 vg/pg these days. Seems to wick fine. It's not the best wicking for higher voltages tho. I tend to keep my Twist at around 4.0, maybe 4.1. But if I direct drip onto the atty, I can crank all the way up.
I have one juice that is 70/30 vg/pg, and I am thinking and can't really recall it having issues. Again, it's been so long since I had the 100% VG, that I won't really try to speak to it, just nothing stands out, but I can see it. I like seeing the bubbles, so I tap and shake mine often enough as it is. I still believe the -C system is a very good starting place, and will still recommend it to friends. It's very "low maintenance" early on. Just make sure everything clicks into place, and leaks ... I've not had any.
I'm still waiting to see which mod I get out of Uncle's member contest he ran, and maybe from there I'll goto cartotanks. I have one already, but it's got a dual coil carto in it, and well ... not impressed. Gonna pick up some single coils for it soon, and for my Bella Tank, and we'll see from there as well. But I love the easy of changing flavors with the simple -C tanks.