I used a lot of time and found it difficult, but I was 100% sure I got all four correct at the end and got 0 score
Well, at first I just looked over the thing and clicked the button - thinking that's what I had to do to take the test, the idiot that I am. Was surprised to see that I had gotten a score of 78, after which I realised I'd just clicked what I was supposed to click at the end. So then I refreshed the page and this time actually read the instructions, and then actually did the test, finishing with a score of 0. I don't think it's very accurate though, since I imagine it varies a lot depending on your conditions and the screen you're using - plus, like they say in the actual intro for the thing they want you to buy, it doesn't represent the full test.