I really don't understand what function it needs. How would syncing save bandwith? If it copies the rules and updates directly to iCloud instead of to my iPhone this still requires a data transfer from their servers. The app still needs to check if there is an update, either on their servers or that has been synced to the iCloud, right? Confused.
If a user has multiple devices, the app would download the block list from the devs' server for each of them. Alternatively, it could download the block list once on the first device, upload it to iCloud, and every additional device would download the list from there. So if, for example, the users have on average 2 devices, it would cut their server bandwidth in half.
But as I said, it's just a theory. In any case I don't think it's reason for concern, since the app cannot access anything outside its own container on iCloud.
BTW, I'm not seeing anything related to Admop in my iCloud drive for some reason. But I will not pursue it any further since the lack of whitelisting disqualifies the app for me at the moment.