I just picked them up today and am sick as a dog, so I have only briefly checked them for fit and seal. On the few songs I played, lower bass seemed a little more prominent due to better seal and the highs are better than any of the stock tips that come in the box (and equal to my modified tips), due to deeper insertion and larger bore. Seems like they will be a complete win once I get used to inserting them faster. And if Westone ever releases a UM4X, they'll fit those too! Definitely a recommended investment if you love your W4's.