Give users the option to opt-in for notifications:
Set the priority of notification methods. For example, if a customer sets their WhatsApp number and Pushbullet token, you can set the plugin to prioritize free notifications through Pushbullet.
Require new users to enter their numbers/tokens.
Some features can be enabled/disabled from the settings page:
Logs only mode: disable all notifications. Logs are still generated as if they are being sent.