My Take
As a teaching tool it is good to help cement knowledge once it has been taught. I'm not sure it works on its own as well as the progidy maths does but it is new so hopefully the content will get more and more complete.
How I Use It
Using it with small groups initially helps you to get round all the students so they can get used to logging on and being able to navigate around the game.
Then once everyone is used to it you can use if for whole class learning, as a starter activity, for homework or as a treat if students have worked well.
They can also use it anywhere they are so it's useful for a lunchtime or aftershock activity.