Below are some good questions you should be asking when looking into SD-WAN.
Ask your vendors:
Do you have any evidence demonstrating the ROI of your solution?
Can you migrate seamlessly to an SD-WAN infrastructure?
How will your solution integrate with non-SD-WAN infrastructure?
What capabilities do you have to support a hands-on pilot or testing in my existing legacy or hybrid WAN environment?
Do you have validated and certified security offerings (FIPS 140-2, CC,or Suite-B)?
WAN is a long-term investment. What is the scope and scale of your support model? And the maturity of your solution and your company’s longevity?
How open is your solution?
What new skill sets and hardware or software resources are needed to deploy and support your solution?
How broad is your partner ecosystem?
Requirements for Technology Assessment:
Architecture
What is the minimum and maximum number of branches supported by the vendor’s solution?
How is the interoperability between SD-WAN and non-SD-WAN environments?
What is the solution’s platform, for example, physical or virtual, appliance or software?
Which native Layer 3 to Layer 7 network services are offered or integrated with?
Management
To what extent does the solution support northbound API for third-party management or control applications?
Security
How is direct Internet access (DIA) supported, and which security services does the solution offer or integrate with?
Source:
https://www.cisco.com/c/dam/assets/sol/trends/sdn/sdwan-primer/images/sdwan-requirements-checklist.pdf