Yes, I use an exercise ball. I love it, probably one of my favorite ab exercises, the other two being ab rollouts and hanging leg raises.
Stir the pot works anti extension, and rotation at the same time. Its very challanging if you do it correctly, even though it looks easy. Moving in bigger circles, or changing your foot position makes the exercise harder or easier. I know Stuart mcgill (low back specialist) recommends stir the pot as well, for back rehab and low back injury prevention. He has it in his book as a adcanced plank progression. So thats probably another good benefit!!