No contest - Fortinet is Enterprise ready and a good replacement. More expensive then Ubiquiti, but in the areas we've tested them, the performance (and ease of installation and configuration) makes it worth the price.
Fortinet offers great Security features and is one of the leaders on that, and integrating Wireless LAN infrastructure with Access points proved to work rather seamlessly. Ease of management, single platform and ability to customize licensing as per needs were elements in favor of adding the Wireless LAN solution from Fortinet to our security portfolio.
Ubiquiti is well suited to not just indoor WLAN access, but also outdoors. In fact, the range of the outdoor applications, while maintaining throughput is astonishing. I would say this is not a solution for a 1-5 person small office, due to the costs.
In the web portal, it would be nice if you could create a customer, assign that customer all the devices in the solution, and have a single pane glass to manage them all. Right now you need to access different web links to manage the devices.
The security feature set could be a bit more sophistication, like an Arista AP which polices the air.
Management of devices has become much simpler with the UNMS application, but personally, I would like to see some AirMax-like devices from their Unifi line where everything could be managed from an Unifi controller.
Most Ubiquiti devices are 24V PoE, which is the bane of my existence. I have had several devices fried when staff plugged into standard 48V PoE. They generally don't fail catastrophically, either. You just get strange issues that are difficult to diagnose and eventually need to replace them.
Devices seem to have trouble with many patch cables/switches. Make sure you certify any patch cables you make and don't over crimp.
Sending devices from the factory with same 192.168.1.20 IP instead of DHCP makes it a pain to bulk-setup devices.
Ubiquiti makes great Access points at various tiers provided far better coverage and throughput than consumer-grade wireless repeaters and routers. We have not had any performance complaints from guests or from the administration who use the wifi on a daily basis.
Fortinet offers excellent support. They will work with you until the solution is doing what it is designed to do, within its capabilities. They also do an excellent to follow-up with the end-user prior to closing the ticket.
Ubiquiti's support is basically non-existent by design. However, their forums are a great resource if you are willing to do the research and ask questions. Keep in mind Ubiquiti sells hardware, not support so the responses will be from the community of professionals also using Ubiquiti just like you.
as a stand-alone product, the Fortinet wireless LAN solution isn't the most powerful, nor compelling out there. Others, like Cisco Meraki, offer great products, with added wifi features at a similar price point, but where Forti shines, is when integrated into a network with firewall enablement such as FortiGate. Overall, it stacks up well with others and is a solution that needs to be evaluated in a purchasing project.
We have used products from Netgear, ZyXEL, Cloudmesh, Datto, Mereki, and EnGenius previously often choosing products based on a specific situation, since starting with Ubiquiti [WLAN] we have pretty much stopped [usage] of all other vendors in the networking field and standardized which better allows us to stock spare equipment. Best part is if you need to replace equipment it is easy to swap it out quickly as the controller also acts as a live configuration backup.
