The Shimano Metrea (U5000 SS) was a self-indulgent styling excercise. A glamorous dusting of supposedly 'hipster' cool was applied to a perfectly functional Shimano derailleur design. The whole Metrea groupset was displayed at the Eurobike tradeshow in a mock up of a New York SOHO loft, all raw brickwork and industrial flooring. Giant engineering companies trying to do hipster cool are only slightly more embarrasing that your dad partaking of an activity that he calls 'disco dancing'.
As such the Shimano Metrea (U5000 SS) is a gift to derailleur collectors - not too expensive, slightly different, slightly interesting and, because it sold so very badly, relatively rare.