You may be confusing purchasing hardware and cloud subscription from the vendor producing the e ink display (Visionect) with the Project E ink device itself, which merely sources it's hardware from Visionect. The linked page is about the Project E ink device (https://projecteink.com/products/e-ink-newspaper-art-display...).
The only place that page mentions a subscription is in reference to news paper subscriptions.
> Data Transfer from Amazon CloudFront is now free for up to 1 TB of data per month (up from 50 GB), and is no longer limited to the first 12 months after signup.
This violates the App Store Review Guidelines 3.1.3(b) [1]:
> You must not directly or indirectly target iOS users to use a purchasing method other than in-app purchase, and your general communications about other purchasing methods must not discourage use of in-app purchase.
The only place that page mentions a subscription is in reference to news paper subscriptions.