My vendor got this information from the maker, sounds a bit sketchy to me but I'm passing it on anyways.
"KSD (Kangside) are one of the companies that claim to be the manufacturer of the VAMO. It is them, Vision and maybe one other company. Personally, I think they all get them from the same factory but you never know with China.
OK. after exchanging a few emails with the sales rep acting as an in-between with an engineer, here's the scoop.
With the V3 and the current batch of V2s they changed the whole 510 connection. The center post has been redesigned. The engineer agreed that when initially screwing in a cartomizer it was going to stop part of the way. At that point it is necessary force it a bit, and that will allow the cartomizer to fully seat in the threads. I did this and he was correct. Unlike with other recessed well mods where you are warned to not over-tighten, with the VAMO you need to twist it in with a bit of force. Eventually the threads seem to loosen up and less force is required."