This is a great game to cement number sense in kids' minds, reinforcing ideas for adding and subtracting. It has some clever visual tricks to help kids understand comparisons between numbers, what happens when you put numbers together and chop them up, what exactly the number "eleven" means, and so on.
It is surprisingly amusing even for an adult - I found myself wanting to unlock the animal pictures - although it's not worth the price simply to use it as a distraction for an adult. This is definitely an educational app for kids.
I was tempted to mark it as five stars, but it hasn't been marked as an educational app in Amazon, so my kids can't use it during their "educational apps before play" time in the Kindle freetime setup. (luckily it is so fun they choose to play it during their play time!) I'm guessing the developers didn't get it approved with Amazon, which really limits the time my kids can play on it, which makes the price feel steeper. But even so, there are few games out there that are as professionally and successfully designed to get these concepts to kids, so it's still worth the price.
But devs, if you are reading this - you need to get it listed as educational!