True. The large diameter housing of W3 + very short nozzle can make them difficult to seal well in the ear. The housing goes flush up against the ear before the nozzle is fully inserted. Arguably a design flaw.
I auditioned both a few months back and love the detail of the UM3X more! I think it's a matter of taste.
If you like big bass, and don't care much for lots of detail, and like the fun sound. W3 is better: ) I have the UM3X and my buddy's got the W3. Well besides the game of chess, we really don't have all that much in common