How I Use It
This could be modeled/projected on an interactive whiteboard attached to an iPad, where students can "help" the teacher play by solving the math problems. Overall though, this is the kind of game/app that individual students would use to practice or hone their computation skills in a fun and motivating way. The game play could be adjusted to Easy, Medium, Hard, and you could also pick the math facts that you want your students to work on or they can self-select it.
I see this as more of a practice/drill tool than a teaching tool. If students need motivation to get better at doing mental math computations, then this could motivate some students to learn them. The more they practice/play the game, the faster they should get in computing, whether it be addition, subtraction, multiplication, or division. Some may complain that there is too much game play, but others can see this as a way to motivate certain students to "beat the game."