Pros: Low noise floor, high value and solid build quality
Cons: Gain even on 1x mode is too high for some sensitive IEMs, input 3.5mm jack is in the front (bad ergonomics)
This is a traditional Benchmark DAC-1 style "wire with gain" sound for a very low price. Not the last word in emotional expression, but the O2 has a very silent inky background and good clarity.
For people new to Head-Fi, you can now get an amazing budget rig by getting this and the EDAC. Pair them with good mid-range headphones like the Sennheiser HD 600/650 and you have a fantastic beginners setup. For those who don´t want to make headphone audio a more serious hobby it´ll even be a good "buy, use and forget about Head-Fi.org" setup.