Pros: Price; might be an improvement over my laptop jack for some (pop) songs
Cons: Not better for all songs
As I noted in my reviews of the Alpen E17 and the O2 amp, those two did nothing that my laptop couldn't do. However, unlike those two products, this thing might actually be doing something. I sense a little more bass and treble coming out of my HD800 which makes some songs a little bit more interesting. Not all songs -- for example, Swan Lake definitely sounds better on my laptop's dac -- but certain pop songs sound better on this.
To give you a few technicals, this has the same DAC chip (ESS9023) as these much more expensive DACs http://www.alldacinfo.com/?tag=es9023/
I don't have specs on its wattage output, but my ears can confirm that it is incredibly powerful and loud, so I would guess its wattage is impressive.
Due to its $40 or so price, this is a no brainer 5 stars.