Looks like just DNS blocking using VPN API. I use a different method for system-level adblocking on ios. I temporarily jailbreak, supervise the device, and install easylist's pac to block connections without an external server. Jailbreak is removed after it is set in place. Guide: https://www.reddit.com/r/jailbreak/comments/dbdb8x/tutorial_...

The only downsides I have seen to this method are it's slightly annoying to initially install and if github goes down (where the pac is hosted), phone network connectivity goes down until it comes back up.