I can sense the effect after demagnetizing with Ayre CD, ie more open, particularly high frequency. I had it on almost every week before I start listening to the music and it's been great.
A must have or not: I would say I can live "without" it as my system is rather inexpensive (NAD 312, Denon CD1015 and B&W DM302). If I don't own it earlier, I might not buy it. However, if you have extra dough to spend, you may try.