The tools doesn't always successfully dump the save file, despite it claiming it does. In fact no indication is shows that the process failed. When saving the dump fails, a file will be present but will be completely unreadable (giving a generic I/O error in Linux) and will make the entire FAT32 sd card partition unrecoverably read-only until reformatted.
The tool is usable, but it's always a gamble if it has locked the sd card's partition or not.