Flatbuffers vs CBOR

I chose CBOR for my site https://kwippe.com - we use it to store all of the artwork and keyword data as compressed strings within a very small JSON structure, only a few attributes necessary to categorize the file. So the files are very small, and load very fast. I used this for over 30,000 SVG files, which I converted to JSON beforehand. All of the JSON is converted to string and compressed via a string compression library, then saved as part of the smaller JSON object that I encode to CBOR.

I've had very few problems with this CBOR system, and it was far easier to set up than FlatBuffers and some of the other binary solutions that I looked at.

I think you've already spelled it out quite clearly yourself. FlatBuffer's strength is being able to access the data without parsing/unpacking/allocation, which can give serious performance benefits in some scenarios. But if this doesn't matter to you, e.g. Protocol Buffers may work just as well.

Strong typing vs dynamic typing in data matters a lot too. I'd only use the latter if I wanted generic data storage with no constraints ahead of time.

Btw, if for some reason you prefer dynamic typing, but would also like to have the performance benefits of in-place access, there is actually a format that combines the two: https://google.github.io/flatbuffers/flexbuffers.html

FlatBuffers is not "proprietary". It may have been designed at Google, but it is open source and relied upon by many other companies.