I just quick tested this plugin. Tried adding Private and/or groups_read_post access restrictions. This got desired effect for Pages and Posts, but not for Media (jpgs and pdfs). Meaning my Media marked with either 'groups_read_post' or 'private' shows to everyone.
I have settings set to allow restriction attributes for all types (post,page, media, etc)
I must be doing something wrong at the basic level?