We constantly improve our app by introducing new features. It takes lots of time and effort to develop and maintain the infrastructure behind these features, so they are available only in our advanced plans. However, due to the restrictions of Shopify payment system, only paid Shopify stores can upgrade third-party apps subscriptions. To overcome this limitation and make the advanced features available for development, trial and partner test stores we're introducing the Sandbox mode. 

The Sandbox mode grants you unlimited access to multiple advanced features as long as you don't switch to a paid Shopify plan:

1) Excel-like editor;

2) browser extension;

3) metafield sets;

Once you switch to a paid Shopify, the Sandbox mode will be disabled and you'll need to upgrade your Metafields Guru subscription to keep using these features.