Hi,
currently unbound service type is "simple" that means the unit is considered started when systemd's fork call succeeds. This is problematic as if you want to start another service only after unbound is running, then you have to poll. If unbound was "notify" service then the synchronization would work as expected.

Reproducible: Always

Steps to Reproduce:
You can try to create service that "Wants=unbound.service" but that would not work always as there is naturally a race. So simply switch unbound service to notify, build it with libsystemd support or otherwise write to appropriate socket and verify that systemctl start unbound.service works, as service without stating "READY=1" should not be able to start.
Actual Results:  
unbound.service is "simple" service

Expected Results:  
unbound.service is "notify" service