Report products missing meta data

add_action( 'admin_notices', function() {

	// Get Batch Of Published Products
	$args = [ 'limit' => -1 ];
    $products = wc_get_products( $args );

	// Output Count
	printf( '<p>%d total products</p>', sizeof( $products ) );

	// Loop Products
	$counter = 0;
	foreach( $products as $product ) {

		// Conditions Go Here
		if( ! $product->is_type( 'variable' ) ) {
			continue;
		}

		// Counter
		$counter ++;

		// Get Retail Price
		$custom_field = $product->get_meta( 'custom_field' );

		// Report Missing
		if( ! $custom_field ) {
			printf(
				'<a href="/wp-admin/post.php?post=%d&action=edit"></a> ',
				$product->get_id(),
				$product->get_id()
			);
		}

	} // End Published Products Loop

	// Output Count
	printf( '<p>%d products checked</p>', $counter );

} );