This app is just a bit of fun designed to give you interesting facts about any integer you type in. It does have some interesting points and is worth mentioning because of the fact that it truly revels in the idea that maths is interesting in its own right (something which many students and adults could well be reminded of).
In terms of practical uses, it might add some extra spice to a write up of a project or perhaps could be used as a starter challenge. (What’s the most interesting fact you can find about a prime number under 200?)
Downsides? Well, many of the facts are obscure and difficult to understand. Some of the facts are a little bit dull too.
Overall, I do recommend this app but it probably won’t be on my main start page.