There remain some suggestions for future version:
automatically sending notif if post is published WITHOUT extra scheduling the notification (very important for planned publishing of posts)
editing different subscribers (select/deselect categories)
shortcode for subscription in order to use it in pages/posts
verification, WHO received/din't receive notification (not only list of sent notifications), especially if no entry in "sent notifications", but subscribers received them
Apart from that: Very good plugin!
Thank You very much!