Peter, there is nothing wrong with the concept at all. At close range they would be similar to getting shot by both of Wild Bills .36 cal. Colts at the same time. If loaded properly.

I don't recall ever hearing about them being used in a gunfight or any other "reality" situation. There have been many great ideas that were trashed by "experts" and a whole lot of junk that became a marketing miracle by the same. Such as the .41AE cartridge. The trouble is nobody checked these experts credentials and simply took their word for who they claimed to be.