there is bug in Newsletter – Locket Content v1.0.1: [11-Sep-2017 07:47:34 UTC] PHP Fatal error: Uncaught Error: Call to undefined method NewsletterLock::check_user() in /public/site/wp-content/plugins/newsletter-lock/lock.php:117
It caused by this function call: $user = $this->check_user();
the function doesn’t exists and it should be actually: $user = Newsletter::instance()->check_user();
Please fix this in next version.
Another minor improvement what can be easily added is parsing of Tags or categories to block. If user submit something like “lock, ” it creates array with two values [ 0 => “lock”, 1 => “” ]. So empty post name could easily pass the condition in lock.php:L115. I suggest to strip empty strings.