I just uploaded some images to SS and saw they have a new bulk edit feature.
You can select a bunch of images (ctrl+click) then click edit - then you can edit the categories and info for all those images at once. Shutterstock was very quick to begin with but this just ads the icing on the cake

The feature appears to be very well designed and acts like you think it should. Ctrl+click to select several images, double click to open one image etc..
I found the feature by going to edit my photos then clicking on the 'new bulk edit' button at the top
Thanks SS