One friend from Forti TAC (former engineer) said that it is like DMVPN (afaik, ADVPN is called in Forti) with a bit SLA based path selection, so it is not "true sdwan".
One time I researched almost all main SD-WAN solutions, what I have seen in Cisco it is rich of deep routing with centralized policy. However, architecture is a bit difficult to understand (different controllers, controller to router and router to router operations, new overlay protocol OMP, its mechanism, TLOC etc.). You should be good at in routing/VRF based networking to understand Cisco overlay routing and operations.
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