I used to use a Nomad Jukebox C. As already mentioned, it records analog, 15 minute tracks that have to be pieced together to get a whole file, and it is limited to short recording times. With 2200mAh batteries the longest time I got was 3.5 hours. The good thing is that it will save your recording when the batteries die. Bad thing is that externally it needs 12v instead of 5v like the JB3. I thought about rigging an external battery, but for stealthing it just wouldn't work. Plus side to the Jukeboxes, the get through security almost every time no questions asked because you just pretend it is a CD player. Some say the Nomads have a "noisy" AD for analog. I am no expert, but for casual taping I didn't have any problems with the sound. Also, as mentioned no onboard gain. Unless the concert is extremely loud and you are in front of the stacks, the recording is going to be very low and you will have to adjust the volume a substantial amount.