You'll find a wealth of info using google .... type : "little dot 2" headphone amp .

I've read there have been some quality control issue with past models, so I'd be cautious buying a used one. It depends on how well you know your "friend" .

Ask yourself if this is something you really want, or is it just because you think you may be getting a "deal" . There are plenty of good headphone amps available, and depending on your headphones and usage, you may not even need one.