When you are not sure of what your database needs really are, use DBaaS first. This lets you try SQL or NoSQL. This lets you explore the encryption capabilities of Oracle versus MySQL. Think of DBaaS like buying a car.
You test drive sedans, trucks, and SUVs, and try different manufacturers and features. You may decide to lease or buy. Always monitor and evaluate the cost of ownership. As your system grows, the operating costs might make sense to drop DBaaS and build an in-house system.