This module uses Field API to support adding additional metatags to content pages.
We investigated this module while performance optimising a Drupal site. While examining the MySQL query log we could see many queries relating to this module for a single page load.
The issue was that this module uses hook_entity_load() to initiate a field lookup on every field on the entity type looking to see if those fields are a metatags field.
On sites that don not use many fields the impact will not be large, but on sites that have very many fields, such as the one we were optimising, this was a real performance problem.