First, the good things. This app has a good look.
Unfortunately, the app does not work well. Every time my kid leaves an exercise, it starts from the beginning, which quickly becomes tedious. It does not allow the student to progress.
User input is disabled regularly to finish a slow animation, so the kid feels the app is not responding. Many simple mis-clicks result in waiting for several seconds for a canned audio to repeat itself.
The hit box on some manipulatives, like the number 8, are unforgivably small and result in the above frustration.
The number tracing is unforgiving in unreasonable ways, and doesnt allow the user to correct well from a tracing mistake. The algorithm for tracing 8 is broken and can easily result in not learning how to write the numbers correctly.
All lessons are presented in the exact same order from no knowledge, to some knowledge. There is no way to customize any of the lessons for someone who is already familiar with the very basics.
Many manipulatives look like they can be handled in multiple ways, but they cant, and it is poor enough that the wrong lessons can easily be learned. The sounds never hint at what the user may be doing wrong. It is mindless.
I would not recommend this as an app for teaching numbers in the Montessori method, as too many shortcuts have been made.