Had the chance to try a friend's Prelude (our ears are very similar) awhile ago, comparing it to many CIEMs and UIEMs, and I can see why it takes #4. Wanted to write something up in case anyone was really doubting like I was before.
Firstly, I feel that it's midrange tone is unmatched in its price range and it even gives the flagships a run for their money depending on your tone preferences. A truly beautiful sound that really clings to you after a few listens, especially going back and forth between the Prelude and something like a Zeus or Samba. Clarity may not seem high due to the warm tone, but I haven't heard an iem at this price that evenly articulates every note within the midrange (no emphasis on one range over the other), which does indeed lead to great transparency and a highly natural sound.
Have to agree with Nic that the treble is nicely tuned. It reminds me of a smoky music bar in a way, very warm and comfortable but not the clearest at times. People who don't listen to genres which require very sparkly treble will enjoy it I think.
The Prelude's weakness overall, however, is extension at the bass and treble regions. The bass, as Nic has noted, really doesn't extend very far and it failed a few bass tests that the higher end IEMs had no issues with (midbass for a single driver iem still kinda banging though, great job Warbler). Treble didn't suffer from this as badly but the rolloff is there. I think it's a consequence of having just a single driver. (On a side note, the soundstage size also suffers from the single driver design I believe..)
All this though, combined with easily above average technicalities (coherence, imaging, etc.) and a pretty good soundstage, leads me to think that as an overall package the Prelude is the king of the under $1900USD category (IMHO, YMMV, 2c of salt...). It could even take sales over more expensive IEMs just with its tonality. Its really that unique.
Take these impressions as you will, but I just felt like I owed it to Warbler to write this, seeing as I was filled with so much doubt over the past few weeks
Really awesome job with the Prelude.