I also have both the NJB3 and the Iriver H120. The batteries for the NJB3 are still going strong, but I have only used the NJB3 for at home recording. I have replaced the 3 year old battery in the H120 with a larger one, so I get about 24 hours of playback time and over eight hours (maybe twelve) of record time.
What I like about the H120 is:
1) USB 2.0 port
2) Long battery life
3) Small size
4) Replaceable battery (about $18 dollars)
5) Rockboxable with customizable firmware. My version has a recording histogram.
6) Long lasting remote control. I have had three NJB3 remotes fail.
7) AGC options to avoid clipping
8 ) WAV, mp3, wavpack recording formats
9) Fairly active user community
10) Clipping light option. Tells you if your signal clipped.
11) Adjustable gain per input channel.
12) Volume adjustable during recording.
13) Rockboxed H120 is an extremely usable DAP.
What I like about the NJB3 is:
1) Real time clock to date recordings.
2) Replaceable cheap hard drive.
3) Rugged build
However, I have added a real-time clock function to my H120 by adding a RTC chip and a customized Rockbox firmware to support it.
Currently, I only use my NJB3 for at home recording.