I did not sit for this particular test, but a friend very recently did.
This test, which I am sure you know, is different than the regular test that you would do in the BCG office (I think its called the BCG Potential Test?). In a sense I think this resembles more closely to a regular case than a PST.
You will have to do it in a laptop and you are answering questions from a chat bot. You will have <10 questions, which are a combination of multiple choice and explanation (2-3 sentences 'essay', if I can say that) questions, typically based on your choice. You will close with a video interview where you have 1 min will record yourself of the conclusions in the case.
I won't say it is hard, but again questions closely resembling a case without a chance of asking clarifying questions and often times having to choose appropriate answers from a list of choices can be quite confusing (at least for me). I think the best bet to prepare is just to prepare doing regular cases. I doubt the PST practice would be of much help since it is different than the regular BCG potential test.