The original BMW ADV valve cover protectors are made from alumium, a relatively soft material. Most crashes result in the motorcycle sliding over the road surface for a while. The aluminium will hook with the road surface, which often just rips it off in fraction of a second, therefore exposing the magnesium covers and sometimes even causing even more damage, than there would have been without. The Wunderlich covers are meant to address this problem with their slider at the side.
The Wunderlich covers
clicky cost Euro 149 / US$ 195 a set.