Apparently there was / is a security issue

The plugin author has never demonstrated much interest in maintaining the plugin but some kind soul seems to have taken it upon themselves to fork it to fix a security issue: https://github.com/GDKeller/404-redirected.

I used 404 Redirected with much success for several years, several years ago, but had recently uninstalled it. I am trying it on a staging site; when I activated it, there was a warning banner, “The plugin generated 693 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin.” but otherwise no noticeable ill effects and the plugin seems to do what it has been designed to do. Obviously, your mileage may vary. Fingers x’d