Hooks not working iff im using @ob_start()

It may be that you never flush it as CodeIgniter already buffers it's output. So you are getting double buffering.
https://github.com/bcit-ci/CodeIgniter/b...r.php#L947

But my recommendation are that you ignore this minify and enable gzip compression instead.
https://github.com/bcit-ci/CodeIgniter/b...g.php#L420

If you aren't doing it on server level. (This is the recommended way!)

If you still want it to work, with that slow preg_replace function. You need to fix your redirect(); and add a working exit; as they do work. If applied correctly.
Do you have an example that dosen't work?

You aren't using a caching server I guess? That mean you will be running that replace every time a user visit that page.