Fortimanager in Small Environment?

We have a single site environment (with no plans on branch offices) and standardized on all Fortinet (goodbye aging but useful Cisco and HP):

2 Firewalls (HA Pair)
2 ADC (High Availability Pair)
2 core switches
6 misc switches (4 inside and 2 outside of firewall)
3 wireless access points.

At this size - is there a compelling reason behind using FortiManager?

Thanks in advance for any insight...