Does anyone knows whether Crusting Buttercream (faux Fondant) will turn as firm as fondant? I need to know coz I am putting a few big roses made from gumpaste as a cake topper. Will the weight of the gumpaste roses sink into the crusting buttercream? Please help. Thank you

The crusting buttercream does not get as hard as fondant. Heavy decorations will likely sink into the frosting. You could put your flowers on a small covered cake round, or some other small plate, and use a couple of straws as dowels to support the plate