I've been having a look and the research seems to be solid. You can have a look at the way it's been developed here: https://duolingo-papers.s3.amazonaws.com/other/technical_manual.pdf
Here, you can find a description of the kind of questions and items. And this is what Gemini "thinks" about it.
The CRUE has not accepted it yet, but I don't know what will happen in the future...