<p>How do they compare to the DevXpress ones or the original MSOffice ones.<br>
Are they worth investing time in them (for practical usage now, not academic curiosity which I'll do anyway)?</p>

From my experience, the new ribbon control implements the entire specification as laid out by Microsoft.  The only issue I noticed was a slight flicker when the form was resized which caused one of the sections to collapse or expand.
Worth spending time in?  Definitely, as they are lighter weight and its a matter of time before someone gets rid of the flicker (could be as simple as a lockwindowupdate inserted in the source?).  It doesn't hurt to use the Delphi action manager, from which all is based.