It's surprising to me how long stuff lives on the internet, and how it gets in places I would never have a clue to look. One of my students just sent me a link to a martial arts forum with which I'm unfamiliar, where someone put up several posts I did nine years ago (NINE YEARS?!) concerning Sonny Umpad's centerline roll technique. I'm not going to explain it here when you can go to this site to read what I already wrote (including some questions I answered after the original post). Suffice it to say Sonny is a very high quality FMA teacher and his training for double stick is one of the most 'live' versions of that part of the art I have seen. His method is simple to grasp but complex in its offerings, just the way I like it.
There is no such thing as a "simple" system. There are those that are quickly accessible to beginners, and those that have lots of complexity and variation.
Simple systems force you to look deeply. Complex ones have the same potential, but often students get caught up in the "more" syndrome and never take or find the time to re-examine what they've already got. In the end, a simple system will blossom and you will understand many ways to use it, and the information will be deeply implanted.