It's still a pretty good backup which I've imported to other services before, here's the CSV header row for those interested:

Book Id,Title,Author,Author l-f,Additional Authors,ISBN,ISBN13,My Rating,Average Rating,Publisher,Binding,Number of Pages,Year Published,Original Publication Year,Date Read,Date Added,Bookshelves,Bookshelves with positions,Exclusive Shelf,My Review,Spoiler,Private Notes,Read Count,Recommended For,Recommended By,Owned Copies,Original Purchase Date,Original Purchase Location,Condition,Condition Description,BCID

The CSV export uses both quoted and unquoted fields at the same time on the same record which is unfortunate, but it works.

Yeah, the Python csv package hasn't had problems for me yet.

One unfortunate bug that they seem to have put onto the 'wont-fix' pile is that for many recent-ish books, the 'date read' field isn't properly exported, so if you try to make reading stats you have to cheat a bit by approximating the 'finished date' with the 'book added' date.

Because of this post I went looking at a backup of my LibraryThing data as well (it's "more fresh", been trying to convert) and it seems just as messy; community threads going back years.

The LT JSON export looks well-formed however, the book records I see are quite vast in content/data/metadata and would probably be a nice python fit. I'm not sure if I could import this with the LT webUI, but it's a nice looking JSON backup nonetheless.