Anyone know where I can find even the smallest of fluff on these guys?

They get mentioned in passing in the BFG book in the Divine Right picture and as part of the technology stolen for use in the Idolator Chaos vessel. I've been able to get some brief mentions of Fra-al raiders elsewhere as well as a couple of versions of folks fleet lists, but I'm just looking for fluff really.

IE: What Segmentum(s) of space would they be encountered in, would they ever be enough of a threat to warrant the despatching of a specific task force towards their destruction in a certain area, ect.