The main "feature" is the fact that this product is supported. There exists vBSEO exploits that have not been patched, and with no support for that mod, it's a security risk to run it.
That's not to say that I can guarantee DBSEO is 100% free from exploits, but if we receive a report regarding an exploit, we will patch it immediately and send out a security advisory to all our members / release the fix on vB.org.
Secondly, when we switched from vBSEO to DBSEO on this forum (very very early Alpha), we noticed a 33% reduction in resource usage and page load times on forum.php. Other users have reported either no negative impact, or a positive impact on their performance. The one instance where DBSEO performed worse than vBSEO has since been corrected.
Thirdly, and this is somewhat related to point No.2, DBSEO focuses on core SEO features rather than adding extra bloat. We've also opted not to include vBSEO features that are no longer relevant in today's market, such as trackback/pingback. There used to be a time where blogs reblogging your content meant increased search engine rankings, but this is no longer the case. Today, having your content shared to social media sites is what will work for you, due to it not really being possible to automate sharing content to social media sites.
In summation: DBSEO is under constant development, is more secure, may perform better depending on your specific setup, features today's relevant SEO features and doesn't contain features that do more harm to your SEO than good.