Hybrid SQL / NoSQL Application

I’m debating whether to split my data between two databases, one storing main user and ‘product’ information (MongoDB) and the other storing transactional/financial information (some SQL db).

For example, users can invest in a product thereby generating a transaction record. Products also have performance records that will be captured monthly/quarterly.

All this data should be easily reportable on a monthly, quarterly basis. I was thinking of accessing the relational data via REST API calls once the user gets to that specific page. It does not have to be reactive.

Anyone have any thoughts on this or have done something similar? Should I avoid this approach at all costs ?