This is really neat and I had thought about doing this when I acquired a new Android device that I don't have root on.
Alternatively, a program was made to host a DNS process on the phone in userland that downloads blacklists as well as uses external well known nameservers. Then use build in VPN client to redirect all DNS queries through to the daemon. DNS66 has been doing a fine job since I started using it last week. https://github.com/julian-klode/dns66
I also use this and prefer it to DNS66 because I can use a hosts file rather than just changing the DNS server. Both work well though. Oh, and both are open source!
Thanks for pointing out this open source tool! There are many with similar functionality but none of them are open, and I don't trust closed source when it creates a VPN tunnel :)