I ordered some novas and then read all these bad reviews on them... was ...... I wasted my money. But when I got the thing I was super impressed. Its become one of my favorite tanks. I normally use the vision style cleros and the mop head clearos. The vivi mini nova I got ever leaks and always gives a good throat hit. Once the liquid gets down to 25 percent left it has a harder time getting the juice to the coil, but I have the same issue with my vision clearos.
It does sound like there are some fakes out there, because some people love them and have no issues and others have nothing but issues.
I picked mine up from gotvapes.com; they sell the real deal nova stuff on that site. A lot of it might come down to juice as well. Since I ordered better juice (heathers heavenly vapers), all of my clearos and tanks seem to work better. I'll never go back to any juice with more than 30 percent VG in it.... VG is so thick its hard to wick good and you can't vape hard with it. 70/30 PG/VG mix works grate. I've even got some 80/20 that works even better. I'll use pure VG for dripping, but not for tanks.
One thing I will say negative about the nova is it had a bit of a funny taste for the first tank full, but after that its fine. I've encountered that was thing with the vision & generic clearos as well. Some so bad I had to soak the things before using them for the first time.
PS: I've only been using the nova for about 3 weeks, so maybe everyones issues start happening when they get old. Time will tell for me, so far so good.