For those using the prior version, there's a bug - if you had the plugin installed from before, the NEWSONLY_SUBSCRIPTION_HEADER config had the values 'on' and 'off' (not 'true' or 'false') so you'd have to update the code or update the database. The code checks for this value are inconsistent - ./includes/modules/bootstrap/subscribe_header.php checks for 'on' and the others check true/false so check carefully.