Westone UM1 has a more neutral sound whereas the
SE215 SPE (blue) has a fuller sound and extended bass - natural characteristic of dynamic driver.
The sound quality is neither muddy nor overly bright. The bass, while not exaggerated, is remarkably pronounced for such a small driver.
On the SE215 SPE, the clarity is improved as compared to the regular version - giving it a much cleaner sound and most importantly, the extended bass depth. It is much enjoyable to listen to the SE215 SPE especially when it comes to rock music.
Having detachable cables for the SE215 SPE is a plus as well, I would recommend the SE215 SPE for something more fun and dynamic.