Have seen considerable text written about Xpel, Invinca-Shield, and Stongard. Does anyone know if one is better than another? It seems that there are considerable price differences between them and it makes one wonder why? Is it worth having one of the three installed or not? I asked my local BMW service manager about it as I see it advertised in the new BMW Assessories Catalog. His advice was to stay away from it as it eventually curls up around the edges and just isn't worth the money. Comments/Advice please.