If your page shows momentarily before the block redirect, it means there is another script in your website preventing the block code from executing before your page attempts to load.
Ensure our block code script is placed just after the opening head tag in your website.
<head>
-- Our block code should be the first --
-- All other scripts in the header should be placed after our script --
</head>
<body>
-- Your website content --
</body>