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It doesn't always save costs, admittedly. I tried it with the Monitor Naval Vessel and despite cutting 10 tons of weight, the result still cost a quarter million more than the ICE model.
Really, as long as there is an unbroken line of people calling themselves "Clan Nova Cat," it doesn't really matter to me if they're still using Iron Wombs or not. They may be dead as a faction, but as a people they still exist. It's not uncommon in the real world, after all.