50% or 0% are both interesting goals, but the headline implies that the website is some test of free will. If you get 0%, then it shows there is an algorithm that predicts your performance, and the Kolmogorov complexity is finite. That algorithm is the inverse of the one the website is using.
If we conflate "free-will" with "ability to generate truly random sequences" then the goal should be to generate a completely incompressible, unpredictable sequence, which 50% would probably be closer to.
If we conflate "free-will" with "ability to generate truly random sequences" then the goal should be to generate a completely incompressible, unpredictable sequence, which 50% would probably be closer to.