I tried to use git annex assistant: I can get files to be backed-up on a server, but when doing sync between 2 different machines it has never worked (I've been doing the xmpp-setup dance multiple times, and it's especially painful due to having 2factor auth enabled on google)
I'll have to try using plain git annex from the commandline to try to understand what is going wrong (I already used it to clean some repositories that the assistant was refusing to delete)
PS: I tried it with 2 machines in the same LAN (both linux... though one of the 2 distros had a slightly older version of the git-annex package)