It still works if you manage to find an intact Muvo 2, also I don't see why using the 4gb Hitachi MD outside of the Muvo 2 will break it.
Actually that Pocket PC Magazine rated the 2.2 GB Magicstor MD as the best editor's pick hardware in Feb/2004 due to the low price and high reliability.
http://www.pocketpcmag.com/newsl_NPR/editorspicks.asp