> You won't be able to use the data outside of Rust and you're probably tied to a specific Rust version.

This seems false after reading the book, the doc, and a cursory reading of the source code.

It is definitely independent of rust version. The code make use of repr(C) on struct (field order follows the source code) and every field gets its own alignment (making it independent from the C ABI alignment). The format is indeed portable. It is also versioned.

The schema of the user structs is in Rust code. You can make this work across languages, but that's a lot of work and code to support. And this project appears to be in Rust for Rust.

On a side note, I find the code really easy to understand and follow. In my not so humble opinion, it is carefully crafted for performance while being elegant.