I'm more inclined to trust Spielberger, anyway. Schiffer doesn't just publish anybody.
"Spielberger, a leading expert in the field of German military vehicles. . ." doesn't quite say it all. Not only did Walter J. Spielberger serve as an Elefant crew member, but he was also one of the design engineers of the Elefant project. He is considered by many to be the expert on German armor of the WWII period.