It will work ok for loud shows and not so well for quiet shows. You'll find that you need to boost the levels afterwards, and that can bring about the hard drive noise. Although my sig says AD20, I haven't even run it yet. I've done a bunch of CSB>JB3 recordings without it (subject to the problems above) and when I saw a good deal on an AD20, I jumped on it. As I said, I haven't run it but it is a really nicely crafted piece of gear and costs <$200 used.
The a>d in the JB3 ain't too awful but the gain is an issue with mics plugged in directly. I'll put up a song that demonstrates it all - how good the JB3 can sound along with the hard drive noise. This was recorded at a theatre, show was not very loud, CSB>JB3 line-in @ +12dB. I was in the 2nd row off to the side - most sound is from the stage monitors and direct (especially the drums). I was seated and the mics were shoulder mounted - what I like to call the 'body baffle' - a little bit of flesh between the mics and the noise from behind. The p.a. was way above - we were basically under it. Then I had to add another 23 dB afterwards, for a total of 35 dB of gain. It will help put the hard drive noise into perspective - it's there on the quiet passages (listen at 0:09 for the beep). Once you've heard it, you'll continue to hear it throughout.
-edit - link down - pm me if you want itAny one who's interested - give this a listen - it's an awesome Bruce Cockburn tune! And although this recording does have issues, there's no denying the 'natural' sound of a pair of omnis in this cardiod dominated world