Fortinet itself is a well know name in managing the firewall and security. With FortiExtender they gave an excellent solution for increasing the connectivity within the organization and helps to manage it with the cloud-based system. The implementation helped to achieve lower latency and higher efficiency for the users in the organization.
When there is a problem, the errors provided in the GUI are unhelpful. In order to have a chance of solving most issues I've come across, you need to be comfortable with the CLI.
Most products in the FortiGate product line do not offer POE power support. The Extender requires POE and has no internal battery. This requires a switch or injector between the extender and the firewall. In the event of a power outage, you lose the extender if you don't have it plugged into an adequate battery. As it's installation can be in a different location then the Fortigate, this can be a hassle.
Both the Fortinet FortiExtender and the Fortinet FortiGate products are great because they provide the agency with secure technology and allow for good network speed and security. Fortinet FortiExtender and Fortinet FortiGate are both costly and a better lower cost solution would be better suited if the budget restrictions of your agency are very important for you.