My recollection is that the HR24-100 and -200 have a newer/advanced Broadcom processor, in contrast to the HR24-500 version that uses another vendor's new processor.
Not positive about this, but a couple members have told me that the 200 has a more advanced processor than the 500. I have both and the 200 does seem to be less buggy than the 500. Both have WD EVDS 2TB externals on them in Thermaltake docking stations.
Don't take this as Gospel, both members weren't positive about the processors. But the 200 I have is definitely less buggy than the 500.
All operate in virtually the same way.