This plugin works well for my admin account, but I only use that account for maintenance tasks. My primary account is an "Editor", so any "unsafe" mimetypes I try to upload failed. Revisiting 'Settings > Allowed Mimetypes', I can see the 'User level required to upload unsafe mimetypes' is set to "Admins only". I changed the setting to "All uploaders" and clicked the Save Changes button. The page refreshes, and the setting has already reverted back to "Admins only", and sure enough, no change has taken place.
This is a clean installation of WordPress with no other plugins enabled.