• Its method of scanning a folder instead of handling files in a normal manner is profoundly inconvenient.
• It doesn't accept files dropped on it, and .flv files assigned to it in the Finder's Get Info panel receive no icons.
• It can't handle Japanese filenames, not only displaying them as gobbledegook in its list, but also refusing to play them until they're renamed.
If the author would give it a normal user interface and let it access files like a regular application, this would be convenient to use. As it is, it's just useable.