The sole purpose of this add-on is to give a little bit of love to Project Managers that are keeping versions in sync between projects. Now you can update only a single project and we will propagate the changes for you.
The Version Sync add-on will instantly propagate version changes to all linked projects, allowing developers to select the appropriate fix version(s) as soon as you are done updating the version roadmap.
Full Synchronisation will keep versions completely in sync with their "Master" project. Rogue versions will be removed. If this is to rigid, choose the event based synchronisation to only update specific changes.
I can recommend both the plugin and their support for it.