DOWNLOAD BETA: http://zabkat.com/test/declone_setup_beta.exe
as for new features only a few trivial additions after your feedback:
* program option to IGNORE MEDIA SIBLINGS (=located in the same folder) when checking for similar music/video
* invert marked menu command (filterbar section) flips check state of all visible items
* added keyboard shortcuts for most toolbar buttons
* MERGE GROUPS menu command, meant to combine consecutive groups into one (e.g. SELECT items from groups 20,21 and 22 and right click to merge them into group 20). This merging allows you to delete more items, bypassing the "1 item per group must be unmarked" constraint.