This is only a useful system if you can trust that failed databases simply disappear.
In failure modes like accidental delete without WHERE clause, or a write that corrupts the validity of the business logic, it's useless, as you can watch the logs to see all your slave machines keenly and unquestioningly repeating the issue.
We had that at my previous job, fortunately for some reasons the slave was delayed by like 10min, it saved us from a very very serious problem, especially when you do backups every 6h.
In failure modes like accidental delete without WHERE clause, or a write that corrupts the validity of the business logic, it's useless, as you can watch the logs to see all your slave machines keenly and unquestioningly repeating the issue.