This whole case is very strange. From my point of view (I studied law, among other things) there is no justification to take action against this tool or its authors. There are various contents on Youtube, whose license allows downloading and offline playback without any problems. What is allowed with the tool in a specific case depends on the country or the jurisdiction of the user as well as on his actually intended actions. What has happened here obviously goes far beyond what an author or his or her copyright collective may demand. The whole thing looks more like a charade.