Could be great
This is the best-looking app of this sort that I have seen (other than the choice of handwritten/chalkboard font for the numbers), but something tells me the appearance took precedence over the importance of utility. The instructions for methods are sometimes unclear, and not only because it looks as though the person who wrote it was not a native English-speaker. Sometimes crucial words are omitted. Sometimes its just unclear whats being said.
Additionally, it is my opinion that the app could use some expansion regarding how one is able to test oneself. Let the user test him- or herself incrementally with each step as they begin to understand it, or allow the user to include or omit the methods used in the testing portion. Otherwise, it requires the user to master and understand each kind of method before feeling they can challenge themselves effectively. Otherwise, this is a great app, and a beautiful one to boot. Id love to use this more often if I could seem to have it work more in my favor as I learn and test myself with each method. It certainly had great potential, and I look forward to seeing how/if it changes in the future.
Ecp84 about
Mencal - Mental Math Tricks