function my_wpf_filter_registration( $user_meta, $user_id ) {

    if ( ! empty( $user_meta['newsletter-hub'] ) && in_array( 'No', $user_meta['newsletter-hub'] ) ) {
        return null;
    }

    if ( 'No' === get_user_meta( $user_id, 'newsletter-hub', true ) ) {
        return null;
    }

    return $user_meta;
}

add_filter( 'wpf_user_register', 'my_wpf_filter_registration', 100, 2 );