As a native English speaker, the Kanji-only Google map app that comes with the iPhone is a constant source of frustration. Japan Map provides detailed maps, reasonable load times, and - best of all - Romaji names for cities, railway stations, streets, and important buildings.
While some reviwers have complained about slow load times, I find them comparable to the standard Google map app.
Why only 4 stars? It does have some issues with location lock in more rural areas, and the address search can be a bit tough to navigate through when looking for smaller, incorporated, municipalities.
Worth $9? Probably not... But, in my opinion, - for anyone who spends any amount of time in Japan - its worth every penny of the $5 sale price.
lumchanmfa about JAPAN MAP by itsumo NAVI