So far, Codz, my Vivi Nova hasn't leaked (I got a second one, and will likely phase out my protank II with it). The protank doesn't seem to care how full it is, it just wants to leak. I suspect maybe their O-ring sealing system just doesn't work - or maybe I have bad O-rings.
What really ticks off me about the protank is that I have to upend it to fill it from the bottom, and then of course it will leak a bit from the top when I do that. (That would be tolerable of course in the greater scheme of things - my biggest gripe is the leakage that occurs during normal vaping.)
I also suspect that coils don't work as well as wicks for vapor production.
On the other side, the Vivis have a plastic mouthpiece, which isn't particularly to my taste, and they don't have that metal "collar" that the protank does which protects the interface between the tankomizer and the battery. I wish I could buy the collars by themselves, but I can't.
All in all - even though: (1) the protank is "built like a tank" (pun intended); (2) I generally prefer glass & metal to plastic for both the tank and the mouthpiece; and (3) I love that metal collar ... leaking during normal vaping use w/o duct tape around the tank is unacceptable, and the duct tape itself is borderline unacceptable.
So the vivi nova wins by a couple noses of so over the protank 2 at least IMHO.
Anyway I'm going to get a third battery to support my habit of switching back and forth between strong menthol and full-flavor tobacco juices, so it's time to stop spending money on equipment. I think I'm out almost $150 (= 115 quid or 100 Euros I believe) so far not including batteries and juice ... so it's time to stop fiddling with the vaping interface and move on to DIY. I figure it's going to take me another few months before I have everything to my liking.
On the other hand, I don't really use analogs anymore, so that's what really counts!