The beta version(currently at demo) is for testing new pull requests and review functionality, it's for now just for mercurial (ui is not finished so the buttons are visible for git for now).
Currently we need to polish the whole review flow and UI for mercurial, right after that goes stable we'll implement the same thing for git, all functions and the whole pull requests / codereview system are prepared
to support both git and mercurial, but for now the active diff between two repos is working only for mercurial.