well I have no experience with this unit, I don't use one and don't know anyone who does. In fact, I 've ne3ver heard of a concert taper using one. That's not to say it can't be used just that it isn't common.
What I can tell you about many of these sort of recorders from edirol/roland, marantz, fostex, tascam, korg, etc... they are not designed to be used to record concerts. their analog gain sections are not usually structured all that well for recording loud rock concerts. that is why so many of us that use devices like this have them modified by audio professionals like the oade brothers or Busman at Cascade. That's not to say that this device won't work, but that you might be better off using a device that one of those pros offers modifications on. Also this deivce is only a 16 bit device. while 16 bit recording is still a perfectly valid techniology things certainly seem to be moving to higher resolution recording devices. either 24 bit recorders or even DSD records.
As far as this particular device goes there are plenty of other options in this price range that might be a better fit. The marantz pmd671, tascam hd-p2, edirol r-4, korg mr-1000. I'd opt for any of those devices of the cdr-420 any day of the week, because all of those devices are mod-able, they record 24 bit, and have been tested extinsivley in the field. They are all around the same price as the cdr-420. None of them can burn CDs, but honestly I don't see that as being all that useful for a concert taper. Are you going to track out your recordings right on the device? what about any post processing (adding gain, compression, EQ, etc)?
The sound devices units (702/722/744) are all nice units. However they are all also much more costly than any of the other devices. If you've got the money and want a pro quality device you can't go wrong with their recorders... they are well built, have nice analog stages, nice A/D, and top quality support.
I can tell you that calling marantz and asking them to compare their products to a competitiors products will most likely result in them telling you how much better their product is even if it truly isn't. They are a company, and their goal is to sell stuff.