Other reviews seem to be very confused about what this app does. It is not an emulator. It does not play games. What it does is allow users to patch their ROM files with hacks and other changes contained in "patches" distributed online. This is useful for things like translation hacks of Japanese games which were not released in English, and customized versions of games with new levels, among many other things.
It also has a few extra tricks for handling ROMs, like managing SNES headers (patches must be applied to the same type of ROM as they were created with).
The only major missing feature for me is write-privileges for external SD cards; I have to do all my patching on internal memory then move my files to the external SD card. I rated five-star anyway because the other reviews which don't understand what this app is are unfairly dragging down its rating.