At long last, I've updated this application to make it more user friendly than ever.
Now, instead of supplying paths one at a time, you can drag multiple bins or folders to convert to/from the P5 PS3 bustup format.
Also, a new bustup format is now supported! Previously, the tool could only create and extract bustups containing pairs of DDS images. However, not all of the bustups in the PS3 version were actually split up into pairs... the ps3.cpk/font/assist/bustup folder contains small bustups used during dungeon exploration.
Now the program can detect whether the bustups are probably in pairs or not.