Great tool! Bookmarked for future use. Two observations after a quick test:

1) It would be great to be able to choose Size vs Quality on a per image basis. If I'm uploading lots of images, I'd personally like to be able to choose compression settings individually.

2) The tool seems to set the images resolution (Pixels/Inch) to 72. Not really an issue, but it does mean the original image (in my rest a Retina screenshot) and compressed image appear at different sizes in OSX Quicklook, making them harder to visual compare.