Reporting some impressions from Head-fi forum member Catscratch (not just a man whose ears I trust blindly, but also the main “culprit” to introduce me into Hi-Fi over ten years ago). These are his first impressions about the Westone Pro 50, which apparently suffer of bass excess overwhelming the mids.
Here are some excerpts from the thread:

Catscratch:
“Picked up a Pro 50. First impressions are mixed.

Taken in isolation, these are pretty good, though not great. They do sound a bit like an HD650 in a rig that can’t quite tame the bass. There’s too much mid and upper bass and it interferes with the mids. Instrument tones are too warm, and the lower mids are obscured and a bit muddy. On the plus side, though, you have pretty much everything else. There’s more detail than in any universal-fit IEM I’ve heard thus far, the highs are smooth, the dynamics are very good actually – even unamped – and drums and guitars sound great on these. Vocals can be a bit buried in the mix though, and cymbals sound like they’re coming from next door. Though to be fair, that’s how they sound on all Westones.

But when not taken in isolation, these make less sense. For a starter, I don’t think they’re a meaningful step up on the UM3x. Sure, they’re more detailed and dynamic, but they also mess up the mids, and the UM3x doesn’t. I was hoping for an updated UM3x with these, and what I got instead was a totally different canalphone with its own set of problems. And then, there is the price. If these were $400, I’d say hell yeah, go for it if you like bass. If they were $500, I’d say think about it, you will have some entry-level custom-molded options that are probably better. But $650? There’s just no way they’re worth that, at least sonically. $650 will get you an HD600 and a decent amp, which will sound better. $650 will also get you a Stax 2170 system which sounds better still. You do pay for the portability of course, but then why not go with a much less expensive canalphone that’s almost as good, or a slightly more expensive custom that should be much better?

I’m not sure what I’ll do with these. On one hand, they kinda mirror the HD650 in being absolutely great for jazz, rock, blues, that sort of thing, basically anything that benefits from a very warm transducer but still needs a lot of impact and dynamics. On the other hand, acoustic, classical, and electronic music sounds kinda muffled and a bit boring, and the UM3x definitely does better with that.

I will take these over the Westone 4 though. W4 also has warm mids, but the midrange warmth is a result of an upper midrange dip which makes them sound dull and dead. The Westone Pro 50 doesn’t do that, and it has more detail besides. The bass is more controlled on the W4, but that’s about all it’s got going for it. I don’t like any of Westone’s consumer-oriented earphones – but I haven’t heard the W50 and W60 yet.

The comfort is great. It’s the same shape as the Westone UM3x. The memory cables are only marginally less annoying than other memory cables, and I wish they’d ditch them. The stock tips aren’t Comply foamies and are worse, so I’d put Comply tips on these asap.”

In this thread you can find more Westone Pro 50 impressions.