i've run low on sanding discs for my 5" sander. I usually just grab what's at the local big box store, Diablo or Norton, etc. I was looking at Klingspor and see they have 3 different discs. Aluminum Oxide, AZ-Plus Alumina Zirconia and something they call greentec.

The Aluminum Oxide I am sure is pretty much like Norton's discs. Anyone use the other two options and is it worth the cost factor?