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I think it is exceptionally rare! The cat's pyjamas, in fact.
Very few Germans would have been eligible for the QSA, I imagine.
As regard ABO/Iron Cross combinations: The WMBR records 882 Germans who served with the Boers, but only those who fought to the bitter end, or possibly the 44 German POWs or 13 Germans killed in action, would have been eligible for the ABO medalje.