I remember that people were saying the headphone jack had issues, though that was supposed to be resolved in the later versions, I think. I will say, however, that I have one of the older versions, and I personally never saw any issues; it's supposed to be a desktop amp, after all, and the issues revolved around static noises while the jack is being moved around (if I recall correctly).
It's a definite improvement over, say, the headphone out of an integrated sound card, but it's not like you're going to suddenly hear completely different music; you can't have overly-unrealistic expectations. That said, I'd definitely say it's worth it for that price (bought mine for little more than $80), though that would depend on exactly what it is that you need.