Works great!

Perfect little plugin when testing and changing the site layout and media size settings a couple of times. And most of all to delete the no more needed duplicate image sizes.

But be aware that you may have to re-assign a lot of images if you delete the sizes they used to have (that old size is still present in the WP image code). Can be a big job if you have lots of old blog posts with lots of images attached. But featured images is no problem. That is not something wrong with the plugin, it is just how WP behaves.