Get array of posts based on custom field values

Look at the meta_query argument, and the "IN" option for the "Compare" operator.

Your query would look something like:

$args = array( 
      'product' => $product, 
      'meta_query' => array(
          array( 
              'key' => 'primary_link', 
              'value' => array(
                    'home', 
                    'obj_handling', 
                    'standalone_doc', 
                    'advantages', 
                    'weaknesses', 
                    'top_comments'
                    ),
              'compare' => 'IN' )
          )
      );