I had the V500 for a short while and I have a Scan Dual III. I now rarely use the Scan Dual and almost always reach for my DSLR + macro lens + lightbox setup. I did a comparison of the V500 vs the DSLR setup (for 35mm negatives) and they were basically equal in terms of quality. The DSLR setup, however is MUCH MUCH faster and also makes it easier to deal with dust (with B&W at least).
If you're a DSLR-owner, I think
camera scanning is the way to go for all but the most demanding applications.