Pros: Great SQ and build quality, small size, good battery life
I primarily use the Pico at work to listen to CDs and for that it does an excellent job. Occasionally it's used amp-only with a rockboxed iMod or H140. In all cases it is a solid performer. The USB DAC is the main reason people buy it but the amp circuit is no slouch either. The soundstaging is great, notes are sharp and clear. Some people call it warm, I don't find it as such. It may be a tad on the expensive side, but the build quality and value that it delivers warrants the cost IMO.
In my case it's usually paired with AKG 271S or SE 530s pushing Rock/Jazz/Classical. If you have similar tastes, this would be a good choice for you.