I always used light diffuser panels in the past but assuming those are a reef safe material, and the holes are big enough for the frag stem, then it looks like it would make a nicer looking rack than my light diffusers.
I think the only thing that would bug me would be if you're making a rectangular or square rack I don't see anyway to cut it that will give a straight line on all 4 sides. It seems like other than on the outside edge of the panel if you make a cut perpendicular to a side it will be cutting a row of holes in half, causing it to not have a straight line.
Other than that little complaint, it looks like it would be a good material for a rack.
If going into a frag tank then I don't think the scalloped edge would bother as much as it would in a display tank. I eventually took my diy frag rack out of my display and replaced it with a store bough magnetic frag rack, because the diy one was a huge eye sore.