The fact that they don't write that "Shopify’s Carrier Calculated Shipping API" is needed to use this app is not good. Wasted my time and energy and got my hopes high... Not too good of a look imo.
Thank you for the feedback. "Shopify’s Carrier Calculated Shipping API" is a requirement for all apps in Shopify. We have mentioned this both in app listing page and in the settings page of our app. Unfortunately this is a requirement in Shopify.