OH DEAR: CD System Enhancers?

The thread starts: Do gadgets like the Isotek System Enhancer actually make a positive difference to sound quality? They are cheap enough (< £20) Also, I've been to hifi dealers where they have some sort of CD drive gadget that supposedly improves the sound of CDs (resembling some sort of cleaning machine). What are these and are they worth having if you play a lot of CDs?