Switch to Config API rather than State API

While trying to get it working with Paragraphs, I noticed this is using the State API (https://www.drupal.org/docs/8/api/state-api/overview).

According to the docs it seems that the Config API (https://www.drupal.org/docs/8/api/configuration-api/configuration-api-ov...) would be better suited for storing user settings.