WooCommerce add order notes to completed emails

functions.php

<?php
// Add an order notes section to customers' completed emails
add_action( 'woocommerce_email_after_order_table', 'wc_add_order_notes_to_completed_emails', 10, 1 );
function wc_add_order_notes_to_completed_emails( $order ) {
	if ( 'completed' == $order->status ) {
		echo '<h2>' . __( 'Order Notes', 'woocommerce' ) . '</h2>';
		$order_notes = $order->get_customer_order_notes();
		foreach ( $order_notes as $order_note ) {
			echo '<p>' . $order_note->comment_content . '<p>';
		}
	}
}
?>

Not sure if it's a right place to ask, but can you shed some light onto if it's better to use
if ( 'completed' == $order->status ) {}
or
if ( $email->id == 'customer_completed_order' ) {}
to target order completed emails while inserting something into email via hooks?