The UM3x is definitely NOT neutral, it is rather coloured with a potentially overpowering low end, and very dark sounding indeed. Personally though, I do prefer it to most others in the westone line. The W60 is pretty decent, but not something I would pay so much for. I wouldn't even pay half considering the options out there. The w40 &w50, well I honestly don't knw what westone was trying to accomplish with those two models, overbearing midrange, giving a honky plasticky sound, significant treble roll off, and a boomy muddy upper bass which overwhelms everything.
IMO the best in the westone line, by a mile, is the W20, at the very least, its balanced, rather transparent, and somewhat more natural and neutral sounding.
Flat out WRONG!
UM3X has a far more forward midrange than W4/W40. W40/W40 also have a farther extended treble.
Enough said about which is the better IEM.