The plugin seems to work.
I like also the fact that you need to browser upload folders one by one before deleting. It's much easy to organize a cleanup job.
interface needs improvements, especially some feeback on screen when pressing the "delete all selected" button. You know images are deleted only rescanning that folder (and if you have a lot of images it takes a lot of time) or checking via FTP .
A working "select all" checkbox option also very needed, but this edit solve the issue preselecting all unlinked images: https://wordpress.org/support/topic/feature-request-select-all-button-for-bulk-delete?replies=3
another nice improvement could be a way to preview listed images
Anywaym, it's overall good, it works and it helped me cleaning more then a website (while others plugin failed).