Besides that Back in stock notifications for WooCommerce comes with some usefully tools, like:
A subscription contains:
A subscription can not be duplicated. If someone with the same email tries to subscribe to the same products, then the tool shows an warning message.
The confirmation email is sent when a new subscription is successfully added. It can be enabled or disabled, by default is enabled. It accepts merge tags.
Back in stock notification Email:
This email is sent when the product is back in stock to let the subscriber know about new stock availability. It accepts merge tags.
apply_filters('wsnm-modal-form-button', __('Subscribe', 'wsnm'));
Can be used to change the Modal's Subscribe button text.
apply_filters('wsnm-modal-title', __('Subscribe', 'wsnm'));
Can be used to change the Modal's header text.
apply_filters('wsnm-text-cta', __('Subscribe', 'wsnm'));
Can be used to change the subscribe button text.