The product is SHAPE brand Sheet Glass, and the product description says it is "for use in picture frames, replacement window panes, painting, and other crafts and household projects", which I figured was enough of an endorsement for this use case. Not safety glass, but maybe I'll swap it out if the whiteboard ends up getting a lot of use and I keep it around longer term. This is essentially a prototype, so definitely open to changing things as time goes on.