Now, Development time :
About C, beside its slower development time, a real pain is that, from what i understood, you have to restart max every time you modify your object. ( https://cycling74.com/forums/how-to-load-rebuilt-external-without-reopening-max
Perhaps it's just a lack of publicity ?
i'm making it... :-)
* in the WritingMaxExternalsInJava.pdf doc : "For timing sensitive events the js and jsui objects should not be used"