Working great, but it could be enhanced to be more useful.
1. I think what people want to remove from a playlist is,in most cases, files with the same URLs -- in other words, duplicate entries often resulted from manual dragging of multiple files. For this, no need to preview the list beforehand, just one click to delete all duplicate entries. Launching duplicates manager comes later when files with the same tags need to be compared in case, for instance, same songs in different format were added. So it would be great if there was a right-click menu item of "remove duplicate entries" that just removes all duplicate entries without launching any window. For duplicates manager, it could be launched from Tools menu or the current right-click menu.
2. Other options of managing duplicates, such as hiding and deleting, are still needed for playlists when you save duplicates into a playlist to handle them later.