Hi David.
This post on DFL's user forum describes all the changes 1.6.6.1 incorporates. As I see it, all they are saying with that video, is that the new version is able to extract data that it couldn't extract using earlier versions, thanks to improvements in their extraction algorithm.
To assess it's effectiveness, just take a really unstable drive and do a recovery using an earlier version of the program, then repeat with the latest version.