I have passed a few of these massive stones (some were shaped like wine corks - weird). But only after taking malic acid and Chanca Pedra capsules (which again are recommended if struggling to release stones).
I would be interested to know how taking these things led to much more eventful flushes, outside of the explanations given by flush pro-ponents. However giving the same explanation as flush advocates as to how they work doesn't necessarily prove or disprove the flush process, so maybe the mechanisms of the chanca pedra/malic acid are neither here nor there in terms of the overall debate.