I don't know J as well as k, but it seems to map less to trading/finance, my domain of expertise.
I like that k/q is a more traditional language in a sense, you can write code (if you have to) that looks like regular functional/imperative code. J is more obtuse and takes a more mathematical approach that can be confusing.
I do like forks and the point free style though.
Asking because I'm thinking of adding some form of array language to the statistical/data science Racket framework.