NOTES ON CHOCOLATE USED:
I prefer to use a premium couverture chocolate because its relatively high cocoa butter content gives it great flow-ability and mouth-feel. Brands I most often use are Callebaut, Valrhona, Ghirardelli, and Guittard. I avoid the usual store-bought brands like Nestle and Hershey's, as well as candy melts, as they don't flow as well and are more waxy due to non-cocoa butter fat substitutes. They also set a lot faster, which may make it harder to pipe the entire chocolate piece before it hardens.
NOTES ON CUTTING CAKES WITH CHOCOLATE WRAPS:
To minimize chocolate breakage, I use a hot knife (heated in the flame on my stovetop) to cut these cakes. Even so, some breakage is likely to occur - that's just the nature of piped chocolate! But I make the best of it by using the pretty chocolate shards as plate garnish. And no worries about the underlying icing - once exposed, it will still look quite neat.