I just got a used pair of these from a forum member : and wanted to post initial impressions (Still an amateur in IEMs), if it helps anyone trying to make a decision. At best, I can compare it to the Etymotic HF2, which I used the most.
Quality : Build feels good, even though I will use the cable connectors carefully. The cables provided seem really thick and nice, and are resistant to twisting which I appreciate. (8/10)
Comfort : Fit great in my ears, and I can lie down on my side with them on : which is a huge plus. Not as small as the HF2 which I sometimes forgot I had on, even with the deeper insertion, but still a comfortable IEM. (8.5/10)
Sound : Personally, I find them Very V-shaped, not mildly. Especially after coming from the HF2.
The bass is great : impactful and feels really big in size, if that makes sense, close to the ears, and very tall. No boom, and is quick as well. I do feel it leaks over into the lower mids though. Very different coming from the Etymotic, which I love for preciseness, but I would rate it at an equal level based on your preference. In tracks which rely on a percussive track, the bass just shines and takes control of the track in a certain way - making it extremely enjoyable. (9.5/10)
The highs : With the silver filter on, I don't think they are too bright at all - unlike some comments I had read. Are available in plenty, and form a pretty decent image as well. Never hurt my ears, and I can be sensitive to bad treble. (8/10)
The mids : This is the part that disappointed me the most - I had expected a lot after reading reviews. Something about them just feels - off. I am trying really hard to love them, after paying a fair amount (graduate student blues). Some vocals can sound fine, but mostly they just sound very unnatural. Yes, they form a separate image, especially with some EQ, but never quite achieve detail or texture that the Etymotics do. Instruments do not sound like instruments at all - especially pianos. (Almost feel like a flat note, no layers, no decay). Guitar strings sound a bit choked as well. I assume there are some peaks, because sometimes the edges(?) of the sound make it appear more detailed, but compared the the HF2 they feel like sounds generated by a computer. To be fair, some vocals and instruments sound good - but some ranges just don't do it.
(6/10 - could be subjective due to my raised expectations)
Overall : On some songs, that require tunefulness, beat, the K3s dance. They bring the music to life, based off great bass. However, the unnatural mids can be a disappointment, especially on critical listening. In complex music, with many layers, everything seems muddled up - which is confusing to me because the HF2 is a single driver and the K3s are multi-driver and I thought they would do better with confusion.
(5/10 for Classical, instrumental music , 7/10 for classic rock, 9/10 for pop).
Hope this helps. I don't want to sound like a HF2 fanboy, but the mids are just on another plane with that earphone and is in a comparable price range. Now I wish I had the bass of the K3 Pro with the HF2 :/