Good try

This doesn’t seem faster than the built-in wordpress way where you can assign categories by selecting a collection of post, choosing action -> edit -> apply. Also, it’s not workable for me because

1. I have over 8000 posts, so having to go trough hundreds of pages, assigning the categories in unworkable.
2. The posts are of a custom post type, and your plugin only support normal posts.

If you fix these points you will get an extra star for each ??