While you can cut to size, I opted for the coat hanger jimmy rig set up...works like a charm.
A good value product, I drilled two additional holes installing the supplied hardware through them. Then fabricated four additional insulators out of cut aluminum gutter ferrules the stuff you use to hang guttersand regular drywall screws. Make sure you install the fabricated hardware on the external holes of the mantel, away from the main heat. The mantel is very steady this way.
Good quality and still easy to trim. Needs more insulated fasteners to maintain shape when hanging.
Product shipped as promised, easy install, I don't even notice that the shield is there.