Cover your cake with buttercream or ganache, place on a turntbale and spin while holding this edger against the cake. A surefire way to get that sharp edge you're after! Internal sizes: 75 x 100mm (3" x 4") and 75 x150mm (3 x 6").
Make sure to cool your buttercream or ganache in the fridge before heating the edger in hot water and drying. You can finish off with a palette knife, again warmed in hot water and dried.