So my findings so far on the 2 tanks -
The Atlantis has never leaked, the Sub Tank however seems to leak rather randomly from the seal at the bottom. It's not constant and can sometimes be hours without leaking but it has certainly happened a few times. The Glass part of the tank spins freely even when you have done the tank up as tight as possible, I guess that is normal and part of the design.
I had contact issues with the Sub Tank from day 1. It took a fair bit of adjusting of the 510 screw inside my IPV V2 before I could get the thing to fire. And for some strange reason if you tighten the Sub Tank down as far as I would with the Atlantis you get a "low res" message on the IPV V2. It's not a major issue but means you cannot tighten the tank down fully to meet the top of the IPV V2. It leaves a slight gap of maybe 1/32", any more and it won't fire.
So that's the bad points out of the way.
Flavor wise, I would say it might give a little more flavor than the Atlantis. It's a pretty close call between the 2 but I am very happy with the flavor on the Sub Tank.
Vapor wise, I would say the Atlantis gives a little more but again a very close call and it's excellent on both tanks.
The Sub Tank is a very big tank no doubt about that, I don't think it looks stupid on my IPV V2 but it's borderline! It is however fantastic to have a large capacity tank again as I was getting annoyed constantly refilling the Atlantis (of course that problem can be cured by adding this - Aspire Atlantis 7ml Extension Kit
which I might do at some point).
To be quite honest I don't think I could recommend one over the other really. I am very happy to own both. I will be using them both as much as each other.
I am planning on trying out the rebuildable part over the weekend and will let you know what it's like and how the flavor and vapor is with 2 coils.
Edit: Couldn't resist so the RBA is fitted. Giving out some great flavor and no dry hit's even at 50W.