I have Horizontal Conditioning: Get rolling, and Volumes 1-4. Sandra Koulourides is the instructor. For me, they were very challenging, at first. I had to hit the pause button frequently, and they had a big dread factor. I was just determined to do them, because they were so challenging. The results have been great. Check out You Tube, she may have some of them there. If not, just buy one, to see if you are willing to do them. I've read some reviews, they just have too much of a dread factor for some. I now look forward to doing them. (sorta) They do get easier, and someday I just want to cruise through them. She has posted pictures of people that do Ho Co. They have great abs, but they are a total body workout. If you decide to try them, I wish you well, and good luck!
I forgot to add, she does use a step, a stability ball, a body bar (although a weight would work) and gliding discs, for props. Not all of them in the same workout. I suggest you preview, before you buy.