The Pocket Amp 2 is a nice sounding amp offering a lot of value for its price. My phones are all low impedance and the PA2 drives them easily and I suspect it can be challenged by much higher impedances. The PA2 is atypical in being a low voltage amp but its sound does not suffer for it. The PA2 has a powerful sound which is very well suited for high energy forms of music. Contained in a very durable and professional grade plastic enclosure, its overall build quality is very nice. It is very small and can easily be put in a pocket. As far as sound quality goes, suffice it to say that it does produce quality output and beyond that, it qualities are subjective. There are many threads you can search for on Headfi that describe its sonic characteristics in greater detail.
Owing to its low voltage requirement, the PA2 is very economical and convenient to use, making it a very nice portable amp. It runs on two rechargeable NiMh AA batteries which you install when you get the amp. The amp has a built-in recharging circuit and includes the wall wart to recharge the batteries. After installing the batteries, you can close up the amp and forget about the batteries for a couple of years until they can no longer hold a charge. The wall wart can even be used to power the amp from AC, a feature generally found only on amps costing significantly more.
Another major difference with respect to some competing products is that the PA2 cannot be easily modified with optional opamps. The "cmoy" derived products such as the one you provided a link to generally have socketed opamps, allowing the user to interchange them for other compatible opamps, thus tailoring the sonic characteristics. The PA2 is of a different philosophy, being more for the music listening end user who cares little about the technology behind it. Fortunately, the chosen circuitry for the PA2 is very listenable.
With regard to the amp you linked to, not knowing who built it, it is impossible to speak to its quality. Spec-wise, it appears to be on par with a MINT grade amp, which is to say that has a more sophisticated circuit design than the PA2. Build quality appears to be very nice. How this translates to sound quality is again subjective and though more complex, cannot necessarily be deemed to be superior without an audition.
Finally, with the PA2 you have Gary's support which in my experience has been excellent. While my PA2 has been operating as expected in the two months I have had it, I have no doubt that Gary would stand behind it if there were a problem. While the other amp you are looking at appears to be a well made, more advanced amp, it might be a bit riskier from a customer service point of view.
Since this is your first amp, my suggestion would be to go with a Pocket Amp. A new PA2 will cost roughly half of what the other amp is going for. It will certainly give you a strong taste of what amplification can do for your setup. I imagine you could return it if you found it not to your liking, but my suspicion is that you will find it to be a nice entry point into portable amps. For what it offers at its price, its a good deal.
