Thanks for making these files available. I’ll add myself to the list of people here citing them as a helpful study tool.
To anybody for whom this matters: I’m relatively sure at least some of these audio files are TTS, and also relatively sure that at least some of the sentences are objectively unnatural, after running some suspicious sounding ones by a native speaker friend.
I don’t have the skills or knowledge to give my own take on either point, but I wish I had had both of these things on my radar before starting to work with these files and wanted to share the above information with anybody who might find it useful.
Happy studying everybody!