This is my first stationary dac/amp, so my experience is rather limited.
It has the necessary oomph to drive my Hifiman HE-400i's. Granted, it needs an external PSU to do so. But it does work pretty well.
I know the Zen Dac is marketed as a "beginner's item" and... I dunno, I'm pretty happy with it for what I need it for - an external source to run into my big PC to listen to music to. It does sound pretty good. Sure, other dac/amps have more bells and whistles and whatnot, but for my purposes it's pretty much perfect. Setup was actually easy plug & play, and so far I have no issues to report... But then I've only had it for two hours...