I have the Bedini Ultra and the RS bulk demag unit, but don't use either on a regular basis. Any improvement is very subtle. The very expensive Furutech unit is supposed to be the best demag available for CDs, Cable Co may let you try one if you are interested. There is a review in Stereophile on the Furutech, also at 6 Moons:
http://www.6moons.com/audioreviews/audioreviews.html