Do you have any practical experience as well as recommendations in your organization for a financial master data management (F-MDM) product - whether SAP MDG or any others with key features including ERP and other integration, workflow and approval management and flexibility of configuration, chart of account attributes managed etc.? Is so, what are the advantages and disadvantages of that specific product

I am unaware of any enterprise-class MDM platforms that specialize in financial master data management - given all MDM platforms must be multi-domain even to be considered a viable option for most large companies.  All of the major MDM providers are able to support GL/chart of account requirements, and have robust support for all the key capabilities you mentioned in your question.  If your company is primarily using SAP for ERP, then the MDG product would have many advantages over their-party provider given the native integration across SAP-based solutions.  However, while an MDM analyst I would often hear concerns about the lack of flexibility in the SAP solution, and concerns over its usability.  

Would Coupa work for your use case?

I would recommend IFS - https://www.ifs.com/
They have a very complete solution.

SAP Master Data Governance (MDG) is a popular choice for organizations using SAP ECC as their core ERP system. It is designed to centralize and manage master data across various domains, including finance.
When evaluating F-MDM tools for your organization, it's essential to assess how well they align with your specific needs and evaluate the level of effort required for implementation and ongoing support. Engaging with vendors, seeking demonstrations, and consulting with experts can provide you with more in-depth insights and assist in making an informed decision based on your requirements and constraints.

I suggest let first list down all use case running in FMDM, It is largely used for centralization of CoA or more that that and what all downstream & upstream system interfaced with the FMDM. Then accordingly look for a tool.  Also considered SAP ECC roadmap, i am sure your company definitely looking to migrate into S4 HANA. Being largely in SAP, first place chocie should be SAM MDG.