FWIW, I ran a test comparing LLM accuracy with TOON versus JSON, CSV and a variety of other formats when using them to represent tabular data: https://www.improvingagents.com/blog/is-toon-good-for-table-...

I've only looked at one model (gpt-4.1-nano) so far. I'm hoping to run similar tests on some other models but it gets challenging to discern statistically significant differences with better models as their accuracy tends to be a lot better across the board.