Been using a PowerDNS cluster in production for about 5 years using a SQL backend for replication, absolutely zero issues, not a single crash, memory leak etc in that time. The only downside is the API has a single key and you can not generate more, but there are open source projects that can put the API behind a proxy with additional keys/ACL.
Given it can read BIND files, surprised BIND is still the default in many places.
I wrote one such proxy, though mine is not open source: I found relatively easy working with zones and records, and a well-designed test suite helps building confidence that a key for an "account" A cannot read or write into "account" B.
I'm putting "account" between quotes because it isn't a PowerDNS concept, there is just a lonely varchar column in the 'domains' table where one can store some account-related information. To handle TSIG keys I had to extend PowerDNS's data model to represent the association between a TSIG key and an "account".
Given it can read BIND files, surprised BIND is still the default in many places.