The cost is an advantage. You save a fair bit.

In most of my organization, I must disable SSL encryption in a database for monitoring by FortiDB. Once I do so, FortiDB can get to work and monitor the solution. 

24 x 7 database activity monitoring captures all forms of database activity to detect erroneous or malicious activity. Database auditing records all database activity for complete and accurate audit trails, with independent storage for additional security.

When you implement FortiDB in your environment, you get the benefit of three important features: VA, Auditing and Alerting. You can audit your entire database in depth and review the users activity on your critical databases both in real time and offline. This helps you with both debugging and security.