I'd say it's dangerous for the reasons mentioned thus far; drill bit is brittle and can snap with sanding, the distance from the chuck to the disk is to long, and could make the bit more prone to snapping. Also the bit is fluted and the disk could slip to the pont that it not longer is tight on the bit and could sail off. A piece of rod would be a better choice, and again a bit shorter if possible to prevent being easily warped.
Overall, it's a great idea for the small pieces for sure. I may copy it as well.