@mkristian you are the author of both jar-dependencies and jbundler so you are the best to ask: what is the intended relationship between jbundler and jar-dependencies? Are they solving the same problem and one replaces the earlier attempt? Or, no, one is for obtaining the jars and the other is for setting up a gem to use the downloaded jars?
Perhaps write an additional section of HowTo/ReadMe that describes the complete process of writing a gem which uses one or more maven-central artifacts?