I've thought larger bi-folds have an odd aspect ratio for anything but two-app multi-tasking. E.g. there's ~ no benefit for videos compared to non-foldables with half the screen area. Is aspect ratio not an issue in practice somehow?

It's a great aspect ratio for reading or writing.

And it does increase the size of videos somewhat, compared to using the outer screen in landscape orientation.

Yeah videos aren't as big as they could be due to the aspect ratio, they still look bigger though and its enough of a life improvement that I always flip mine open when I want to watch a video!