Does It Work on Photos That Did Not Come From Google?
The .json files are optional. Here is what happens with any ordinary folder of photos.
Google's .json files are one source of dates, not the only one. Photos from a camera or a phone usually carry their own EXIF capture date, which is just as good and is read the same way.
So a folder of ordinary photos works fine. The tool takes the date from the sidecar if there is one, otherwise from the photo's own metadata, otherwise from the file itself, in that order.
That makes it useful for tidying any library, not only a Takeout export: renaming by date, building Year/Month folders, straightening sideways photos and converting HEIC. Free for your first 500 photos.