Nice plugin, works well.
However, whilst it redirects any valid author page as expected, it doesn't redirect from any non-existing author pages - such as:
So someone can still theoretically find out what username's are in use on a site, but trying ones to see which get redirected, vs. which go to a '404 Not Found' page.
I added the plugin to a site to try to improve security, and I guess from my perspective as such it doesn't entirely 'disable author pages'.
I don't know if this could be added, but could be a good addition to the plugin.