This is a very bad device, do not buy! It's thin tape on both sides with a little bit of sand on each side, it fell apart after one session. They probably won't refund my money, just wasted $7.99 plus sales tax.
Pros
Combination of coarse and fine sanding. The double-sided diamond design creates the perfect grinding plan, using 400 grit for a coarse grind before 600 grit for a fine grind.