Pros: Has power, it is almost without distortion (if you can hear any), it's attractive and compact, and the DAC is clear.
Cons: Only found this: the gain of the O2 is not so high, ask JDLabs that they send your amplifier with higher gain. Some high impedance phones lack punch. But this is no hardship. Their other models have more gain.
I came upon the article by the navguy and almost instantly ordered a kit. I was amazed at the sound of the kit, so later I ordered one O2+dac. I am an electronic technician, so I have assembled and purchased many headphone amplifiers and after testing many I am convinced that this O2, the concept of Navguy, is one of the best amplifiers in the market. You can also try the Cmoybb to hear a good bass and the clear sound will amaze you. I recommend these products to everyone. Period.