Ivory weighs in at less than the various species of African blackwood. I read this somewhere in the past, but don't recall where now. Neither substance is listed in my Engineer's Handbook, my usual source for material masses, but it's unlikely that a combat engineer would be required to hoist any significant amounts of either substance.
The lion's head decorations on the keycups are no more extensive (as far as thickness is concerned) than the Leblanc "innovation of rounds bombé, the fat key cups that they favored for a while in the past. In any event, most of these objections of "too much weight" tend to come from those who have never had to heft bass clarinets or baritone saxophones.
I, for the record, think the clarinet shown is not all that attractive. But, I'm not a big fan of flashy, showy objects, so that's just me...