I was looking at getting one of those a few years ago, so when I was at the Broadcast Video Expo I got to try it out properly with my own headphones (BeyerDynamic DT250 and DT100), and my own mics (Sennheiser K6/ME-66, Rode NTG-1, Rode NT1-a), using the built in mics, as well as a bunch of other equipment at the expo and compare it side by side with similar devices.
In the end, I went for the Tascam DR-100 instead. It was the same price at the time, but much better quality (noticeably better), analogue input recording dials (much easier to adjust as you record than digital up/down buttons), cleaner sound.
The DR-100 also has an extra battery compartment for a pair of AA batteries. So, if your LiIon battery is running out, it'll temporarily run on the AA batteries while you swap out the LiIon for continuous recording.