Network activating the plugin does work. There are no menus added, so you won’t see any. As stated under the “Installation” tab at (http://wordpress.org/extend/plugins/edit-author-slug/installation/), you can find the extra settings under Settings > Permalinks, and Users > Users/Your Profile. However, this plugin was developed to work at the site level, so there are two things to keep in mind:: 1) you’ll likely have issues with saving options (something I plan to address in a future release), 2) since there’s is only one user table, if site #1 changes a user’s author slug, this will change it network-wide. This will occur again for site #2 of that user, and so on. There is a way around this, but I haven’t yet decided if it’s worth the effort.
I dug into this and found that settings save without issue, so the plugin works fine when Network Activated. However, the issues with the user_nicename changing sitewide still remains. Again, I haven’t yet decided if the gain is worth the cost at the moment.