Pros: Crisp but not piercing highs, adequate bass, good sound stage, Logitech customer support is very helpful and proactive
Cons: mids can seem a little flat time, cheap look and construction
This is my first review so keep that in mind.
I bought a pair used UE 900's at Cex, an electronics resale store in San Francisco. I was cleaning them and pulled the wrong way on the MMCX connector and the freakin' right unit came apart and ripped the internal wires apart. I contacted Logitech tech support and was shipped a complete UE 900s for a replacement! They were quick and helpful to respond, much better than I was.
So, this review is for the Logitech UE 900 and Logitech UE 900s units.
These IEMs really excel at representing distinct highs. Cymbals, falsettos, and all high frequencies sound crisp and clear. Until I found the right ear tip, it was on the verge of headache inducing. These IEMs really require the time to find the right ear tip.
There is low microphonics in these. They are almost silent with no music playing.
Bass is present but does not feel compressed or mangled. For me it's just enough.
Acoustic music sounds great with these. Vocals and guitar really shine through.
The sound stage feels medium-ish. The canal is wider than say Shure or Westone IEMs. Not sure if that completely the reason, but like my Sennheiser IE80's it feels pretty full.
Mid frequencies are really not as noticeable and sometimes get lost. Female vocals, electronic music, etc. sometimes are not be optimal for these. They are not absent either. I wish it was just a little more.
The construction is sh*t. For real. The cable and housing, while actually somewhat durable, feels fragile. I only sit and sometimes walk in these. Actually, the cheap construction helps in that people think you're listening to some crappy headphones not realizing that they retail for $300-$400. So you are less likely to get mugged in them :-D
Also, they look a little "Fisher Price" like.
These are currently my second favorite IEM (out of my 5). For the price the treble/bass combo is good, for my tastes.