We've updated the interface when candidates are flagged as duplicates. When clicking on the Duplicate Candidate button, you'll now see a comparison of both profiles side by side. Clicking on the candidate's name will also open the candidate profile in a new tab.
If you choose to merge the candidates, a preview of the merged candidate will be available for review. Here's a screencast of this in action:
At this time, this feature is set to compare one duplicate at a time. If more than one duplicate candidate exists, the next duplicate will be shown once the first duplicate is processed.