They do use LLM to generate the text. I gave a short sentence saying “neighbour blew up my car with tnt” and the resulting letter fictionalized it in 3 paragraphs of fluff with a lot of added details which do not match what I wrote and might be hallucinated and inaccurate.

There’s an additional “legal review” step which I imagine is another LLM pass with “read this letter and ensure it complies with these legal requirements and adjust if not”, at least.

I would not send one of their letters verbatim without perusing and correcting any AI fiction that might creep in.

Then again I’m not in the US so I’m unlikely to ever need this service :)