What it teaches
Spotting a rule from examples. The sequences add, subtract, double and halve, and the numbers are kept small on purpose: a child should be stuck because they have not found the rule, never because the sum defeated them.
This is the reasoning that mathematics is actually made of, and it is barely touched by ordinary arithmetic practice.
How it works
A sequence appears with a gap and numbers to choose from. On a wrong answer the step between each pair is shown, which hands over the method rather than the answer.
What to look for
Ask "what is happening each time?" rather than "what comes next?". The first question is the one the game is really asking, and a child who can answer it will never need the second.