What the hell is SVN?
Subversion.
It's a version-controlled repository that can be used to distribute software. BRL has been using subversion to spread out the latest updates, and rarely use syncmods anymore it seems.
Might be nice if you want the very latest versions of everything, but I guess you also risk breaking things easier since they are development builds.
there's instructions on the forum somewhoere on how to set up SVN and connect to BRL to have it download the updates if you're interested. (I never did set it up myself, syncmods seemed much more convenient to me)