Looking at the terms of use, I couldn't find any prohibiting downloading its content for offline use. As I understand it, there appear to be two semi-related rules:
* Don't make multiple simultaneous API calls.
* Each thing added must be a result of a specific user action. I'm not sure whether this applies to things retrieved from the API.
Also, the dollar per month is for the subscription service, not the purchase of the Instapaper iOS app. Current Instapaper for iOS app users do not need the subscription service, but users who use apps that use this new API will.
* Don't make multiple simultaneous API calls.
* Each thing added must be a result of a specific user action. I'm not sure whether this applies to things retrieved from the API.
Also, the dollar per month is for the subscription service, not the purchase of the Instapaper iOS app. Current Instapaper for iOS app users do not need the subscription service, but users who use apps that use this new API will.