I've never heard of Psyllium being habit forming - psyllium is soluble fiber, it isn't irritating. It doesn't always clear the bowel in everyone though, just some people.
The other two things you listed, cascara sagrada and senna, are both laxative herbs that work by irritating the colon wall. I have read, though, that in moderation they are both useful and safe, the key words being "in moderation". Lots of opinions out there as to what "in moderation" means!