Thanks, I have no idea other than the v2 gives you much more rail to work with and maybe mounts up more solid? I saw a post from RRS mentioning if they had enough interest they'd re-run the v1 but don't remember seeing an answer as to why they stopped making it.
I want the v1 over the v2 because I'm looking to only use it for mounting to a tripod and where it sits would be perfectly balanced, I don't want the entire bottom to be ARCA/RRS railed as I prefer having a stock pad under there.