[codingdave]

Unless you've seen their code and their data structures, we don't know the impact on performance of their technical choices. I would say that there is no black and white answer of what type of product needs what type of database -- it all depends on how you design the solution. I'd also venture to say that with so many databases now supporting JSON as a native data type, you can blend relational and non-relational data as needed within a relational DB.