Too easy to 'cheat' at. Just look at the comments page for the challenge and the answer is usually there. In the end, you just have to take a risk when hiring people, remembering that it is a 2-way street, and that you have to put in effort to make your employees great ones.
Also their tech is not great. I had one question in the python set which would've been very easy to solve if i could import a pkg from the standard library but it didn't let me.