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$bp->loggedin_user->id uses wp_current_user, which isn’t available at that stage of the login process.

The login_redirect filter uses wp_signon:
http://adambrown.info/p/wp_hooks/hook/login_redirect?version=2.9&file=wp-login.php

If you use the passed $user variable, you should be able to echo something.
If you’re using your own code above, try echoing $user->ID.