I think most people complaining about Vivi Novas are using one of the many knock-offs out there. My Vision brand Vivi Novas never give me any trouble. I naturally hold my PV at an angle between puffs which keeps the wicks wet enough for good performance. When the juice runs out at the very bottom, I'll need to swirl it around a little to keep the wicks wet, that's when I'll refill.
The knock-offs can also work well if you're will to tinker with them. Some knock-offs will leak if filled above the hole where the wicks pass from tank to the coil, this leaking can be reduced or eliminated by adding a couple pieces of loose wick material above the coil, like Kanger does with evod and protank heads. When the knock-offs don't wick well, they probably need re-building with better wick material.
I'm going on 4 months now with my first Vision mini Vivi Nova metal tank, It's been filled with Mt Dew flavor since the beginning and the only maintenance it gets is an occasional rinse out when re-filling. It's not in constant use, but Mt Dew is one I vape a lot of. The second one, with Cherry Cola, has been going for about 3 months, also with just an occasional rinse-out.