Say something went wrong, and the company is questioning why you went for an unknown brand. My answer to that would be they offered more value than the trusted brand, also I would have notified necessary stakeholders before making that decision of using services provided by the unknown brand.
You'd have to weigh or SWOT your decision, using a better product from an unknown company that might offer more or from a trusted company (AWS) that offers less. Especially if, the unknown company is offering something the trusted company isn't