I've just started using
Soundtaxi 4.2.1. My experience is it randomly stops converting m4b files to avi files. No error messages - all indications are of a complete, successful conversion. There's no way to know the conversions was incomplete is to actually manually check the converted audio to the unconverted audio to see how many minutes of audio each file contains. I've tried contacting their support multiple times but they do not respond. Support seems non-existent.