Fixed

I used a workaround, but amazingly, a few hours after I posted my review below, the plugin was updated and as best as I can tell, fixed. (I already implemented the workaround.)

Anyway, it was either a superb coincidence or a developer who pays attention! So, give it a shot and see if it doesn’t do what you need.

PRIOR REVIEW (most likely fixed now):
The plugin seemingly correctly identified the correct images and had nice options, but clicking the “Delete Selected Images” button just deleted the information from the database but left the actual files in the directory.

In my scenario, I ended up using Cleanup Images to delete all the child images then regenerated the thumbnails with only the new sizes. That might not work for most.

I’ve left this plugin installed but deactivated because I hope it was just a temporary bug relating to WordPress 4.0. ALMOST there… just didn’t get to the goal.