I've been using Singlemizer for several years,. have tried others to get around two quirks in the interface but always come back to this one.
I don't know if the developer is still working on it three years after the latest version, but if he or she is, I have two suggestions for the UI:
1) When duplicates are detected the list allows you to select any of them except the first. Could there not be a preferences option not allow us to select ANY of the listed duplicates for deletion?
2) It would be useful to be able to select the filename (basename) of any duplicate using the mouse. This would allow finding derivatives or versions of a file which are not themselves duplicates.
5 stars for Singlemizer nonetheless. The best thing about it is its clean, uncluttered interface.