It's kid tested. A lot more challenging from a video game aspect, as the action is fast and furious. It brings a little more speed into the math thinking, which is good for the times tables or other areas where quick mental math ability needs to be developed.
Give it a try and leave us some feedback.
Edit: i just went back to the site and noticed the "video" section, where kids send in questions and the answers are explained using audio and visual responses. Really, do students even need teachers anymore?