Es seguro que .. o está seguro que ?
- When using ser, you indicate that there's a predicate nominative.
In this case, you are are trying to say seguro is describing what IT is = insurance (In this case it becomes a noun)
- While using estar, you express certainty or assurance. (Here it's an adjective)
Es seguro que = It is inusrance that / it is a certainty that
- Está seguro que = It is certain that
Hay gran diferencias entre ‘ser’ y ‘estar’ see this link