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External Database - Backendless or SQL

I am developing a new web application and I would like to have my database outside of Bubble for scalability and security reasons, I have consulted some options on how to do it, the first is to have an external database in SQL and connect it with the Bubble SQL connector, the second option is backendless and connect it with bubble using an API. I want to know if any of you have used any of these options or another and how feasible you see each of these options with respect to scalability.