I've tried it yesterday and I was surprised with how quickly I could do my first JAR file. I tried this JAR file on my PC (Windows8) and my wife's laptop (MAC) and it worked perfectly in both. I think it will be very useful.
Really thanks Erel.
I can confirm that it does. The B4J xml files are produced by the same Doclet as used for B4. Any B4A library with no specific Android dependency, like my ByteConverter and Encryption libraries, will work unchanged with B4J.