This seems pretty cool, so it's free slow cell service in exchange for watching a video ad every hour, with optional prepaid plans for higher speeds/no ads. It does seem that your cellular is only active for an hour after you last watch an ad, which is unfortunate if you want to receive notifications throughout the day.
I wonder how this works, if your cellular gets deactivated, how do you inform the service that you've watched the ad? Particularly if all you have is an app with no access to low-level system APIs like USSD, texting etc. Is it just disabling your access except to a particular IP range and then enabling it back on receiving a HTTP request? Can routing in Telcos even work like that? Or is it DNS perhaps? That would see…
When your quota runs out everything you access resolves to the same address, which is an internal web site where you can buy more data.
And yes, it does not work if you use a custom DNS such as Cloudflare or Google Public DNS, or if you try to reach a HTTPS page. But they don't care, as it's a minority that does this. Android already has support for captive portals, and shows a notification when it detects one.