Both are good.
Differences:
R-09 is 24 bit and records to SD cards.
iRiver is 16 bit and records to a hard drive.
If the DJ is spinning VINYL I would go with the R-09 for the highest quality (24bit). I can clearly hear the difference between Vinyl > 24bit and Vinyl > 16bit.
If they are using CD's or a laptop with 16bit files, the R-09 won't help as the files are already 16bit, then go with the iRiver (unless you foresee recording anything else (live bands) or DJ's that use vinyl.