We used this plug-in for a couple of years before it was abandoned in 2007. Initially it was a very nice editor, but eventually we had to abandon using it because of several show-stopping bugs.
A particularly nasty one was the one where the editor didn't get to see any changes when you updated your workspace from SVN while some properties file was open. If you then later on checked in your version of the file, it looked like if you just deleted the new stuff that came in with the last update.
When you finally detected that some keys were missing, it was quite a lot of trouble to retrieve them from the history and add them again.