Its flexibility is the most valuable because it is a managed service. The good part is that you don't need to set it up. It just needs DNS routing, which is the easiest thing.
Our client had Akamai for certain websites because they were using CDN features. They had NetScaler on the internal zone, F5 AWAFs on the data centers, and no WAF at all in the cloud. One of the main activities of the project was to move all these policies into a single WAF so that we could control and use that as a choke point. That exercise itself was very easy because it was a managed service and F5 Silverline Web Application Firewall does that for you. That's the best thing about F5 Silverline Web Application Firewall.
It is easy to apply policies on-premises. If you have AWAF on-premises and you want to replicate some policies on F5 Silverline Web Application Firewall, other than the policies that it applies by itself, it is easy because you have a team that supports it.
F5 Silverline Web Application Firewall works perfectly fine. It pretty much does everything that an Advanced WAF on-premises should do.