Eric,
Haven't tried the Sheffield disc. I did just try the Densen disc (about 2 weeks after the Ayre/Cardas disc)...it definitely did something, although not as dramatic as the Ayre/Cardas. It might have something to do with the fact that I did the Ayre/Cardas one never having degaussed my system before and the Densen after only 2 weeks of playing. Either way, I'm convinced that they do something. Let us know how the Sheffield disc works for you...