Pros: Non-fatiguing coherent treble, timbre of drums/wooden instruments, quick bass-transients, very-detailed rich bass, powerful subbass, dramatic sound.
Cons: Isolation is lacking due to vented design
I have never in my life heard such detailed and powerful bass in an earphone. What's even more unbelievable is that these earphones are incredibly detailed without ever sounding thin like detailed earphones and headphones tend to do in the mid and upper treble. These are the most tonally accurate earphones and headphones I've ever listened to. And the most bass-detailed headphones/earphones I've ever listened to. I can actually hear bass passages I've never instantly noticed before on headphones, but only could hear on good floor-standing speakers. The drums don't muddy up with the bass guitar, but separates wonderfully. Drums actually sound like drums now; they don't sound like a pencil rapidly tapping against a table (LOL). You can hear what it sounds like "after" the drum (reverb). I can actually hear the reverb and feel the ambience of electric guitars. The soundstage is the best I've heard in a earphone so far, besting even some mid-fi portable heaphones. This may partly be due to its vented design, making these earphones semi-open. Wood instruments sound spectacular. The timbre of wood instruments through these earphones is phenomenal. It is not a "all-in-my-mind" mental thing since I already knew they made the housing out of wood and the speaker is wood-domed(I've heard cellos, violins, etc. all my life, I know what they sound like). The Earsonics SM3's and Audeze LCD-2's sound amazing with wood instruments as well, being able to emote the essence of musical instruments; the SM3's not being made out of wood at all. But the FX850's IMO are more tonally accurate than both the LCD-2's and SM3's with more air/tonal accuracy than the SM3's and more smoothness/less grain than the LCD-2's. Lastly, these are comfortable as hell! They fit my ears perfectly with their angled nozzle design to better fit in one's ears. These are what I was looking for in a earphone or as a matter of fact headphone for a very long time. You got to try these people!
***Add-on: You will need a very quiet source/amp for these earphones as they are very sensitive and you can hear a faint hissing on sources considered quiet. This does affect the treble response quite a bit to my ears, adding a little grain to it.