So here's how they work for addition and subtraction.
A problem is shown at the top of the screen, with blocks on the right to drag across.
You are given the opportunity to check after each task.
It then provides the numbers for you to put in the right place, according to the wording of the problem.
Pressing the resize button will automatically size the blocks commensurate to the numbers.
With the numbers in place, you can they think about the calculation needed to find the missing number. The calculator means that the calculation is made easy - the focus is on problem solving skills.
I often think that even my able year 2s need strong visuals at times; Piaget's theories ring true in that children seem to start internalising at around age 7. With my group of most able mathematicians, one child is very hard on themself and their confusion (leading to distress) is clearly written all over their face when reasoning about number. It's not that the maths skills aren't there, it's the processes that need internalising and reversing that are tricky. Maybe the blocks will help?