I have migrated domains from Cloudflare to deSEC.io the past days, and it's been going very well. It's a German nonprofit which is part of DNS4EU as a consortium member.
for ns in $(dig NS deSEC.io +short); do for ip in $(dig +short $ns); do echo "$ns -> $ip"; whois $ip | grep -i -E "(country|city|netname|orgname)" | head -3; echo; done; done