Works as expected

This is a great application!
The disclaimers are very clear. There could be an option to backup the fullsize images to a downloadable archive, but overall it does exactly what the wordpress media gallery should have an option for already.
I’ve been optimizing images manually for over two decades with programs like photoshop and imagemagick on the server. The best setting for most images, detailed or not, is a setting of 50-60% quality at around 1280px x 1280px for current screens (as of january 2014). If you are looking to reduce the size of your library, then you can afford to reduce the quality a little, and the above setting is perfect.
As said by the plugin author, it is not recommended to use this plugin if you are using wordpress as an archival storage for your high-res photos.