You are in an area full of lots of differing ideas. I call it "marketing" more than solid facts. Kind of like the new idea passed around that there is no truth, just different versions? If I had a rock and it looks kinda/sorta like Ohko stone, I could sell it for a much better price if I called it "Ohko stone" even though it had never been to Ohko! So that leaves us very likely to find an imposter than the real item.
what that item is made of and how it may change your water if really an open subject with lots of answers as there are lots of rocks and lots of different water. So, it depends. If you get an actual hard, true, Ohko stone and put it in water with a fair amount of buffering quality, nothing happens but if you get an eroded limestone that looks like Ohko and put it in water that is soft and acidic, with little buffering, it may shoot the PH way up.
As you have found, there is very little consideration given to what the real stone actually requires to carry the name. It depends on the sellers ideas of truth, perhaps, and that seems to be an ever changing situation.