Yes. First, as far as Sutor goes, this is just one small section of his fetchbuck. I've taken it out of context and placed it here. His assumption is that you'll read his whole book, his system, and use the flail with the same lessons within his system, I'm assuming, in particular, the longsword and staff, which are quite a bit more developed.
There are some other sources for this sort of flail too, ims. But Sutor's system has its own flavor.
As you know, there's a ton of resources for longsword. Surprisingly, there's a ton of resources for (quarter)staff too. The sources, quite literally, range centuries (and in various languages), starting in Medieval and going straight up through 20th Century in pretty much a continuous lineage with a commonality to much of the systems. The sources range through civilian self defense to organized military to flat-out sporting competitions.
While many nations and ethnic groups used the staff, the English really seemed to get their gig on from it and there are more English language sources than not.
Peace favor your sword,
Kirk