Redirecting user

function uc_checkout_download_page() {
// Get the posted result from paypal
$tx = check_plain($_GET[tx]);
$status = check_plain($_GET[st]);
$amount = check_plain($_GET[amt]);
$currency = check_plain($_GET[cc]);
$product_code = check_plain($_GET[item_number]);

$prep_tx = 'PayPal transaction ID: ' . $tx;
// Get the payment receipt

$sql = "SELECT * FROM {uc_payment_receipts} WHERE comment = '%s'";
$payment = db_fetch_object(db_query($sql , $prep_tx));

// Get the order data

$sql_order = "SELECT * FROM {uc_orders} WHERE order_id = '%d'";
$order_detail = db_fetch_object(db_query($sql_order , $payment->order_id));

// Get the product data

$sql_product = "SELECT nid FROM {uc_products} WHERE model = '%s'";
$data = db_fetch_object(db_query($sql_product, $product_code));
$product = node_load($data->nid);

// Check download limit

$download_limit = variable_get('uc_file_download_limit_number', NULL);
if ($download_limit == NULL) {
	$download_limit_message = 'not limited';
	} else {
	$download_limit_message = 'to '. $download_limit . ' download times';
}

// Check download ip limit 

$download_ip_limit = variable_get('uc_file_download_limit_addresses', NULL);
if ($download_ip_limit == NULL) {
	$download_ip_limit_message = 'unlimited unique ip address';
	} else {
	$download_ip_limit_message = 'upto '. $download_ip_limit . ' unique ip';
}
// Check download time limit 
$download_timer = variable_get('uc_file_download_limit_duration_qty', NULL);
if ($download_timer == NULL) {
	$download_timer_message = 'will not expire';
	} else {
	$download_timer_message = 'will expire after '. $download_timer;
}

// Build the output
global $user;
$uid = $user->uid;
if ($uid == $payment->uid and $uid == $order_detail->uid) {
if ($order_detail->order_status == 'completed') {

// CODE FOR DISPLAYING OUTPUT HERE
    
} else {
	$output .= '<p>There is a problem with your payment, please contact our <a href="mailto:support@zweetsal.com">customer service</a></p>';
}

} else {
	$output .= '<p>You are not authorized to view this page.</p>';
}


	return $output;
}

is this code safe to use???