I have gotten a lot out of this app. I can now name all the countries in Africa, for example, either by list or with a blank map. The interface is clean and stable, and I wholeheartedly recommend this app.
But...
Why not add ALL countries? Vatican City's there, but what about Taiwan, Kosovo, South Sudan, and ALL the independent Caribbean islands (why is Anguilla listed but not Dominica, for example)?
Also, it would be nice to be able to choose a specific geographic area--a single continent at least--to study, rather than having to go through each one each time you play.