Returning the the original question, I have to say that I personally agree with Eaton about this. No matter what vocabulary one uses, the chance of a lost neutral and an earth fault arising simultaneously is so extremely small that I really don't think it's really a justification for having a FE on RCBOs.
It's worth saying again that the great majority of UK installations rely on RCDs, rather than RCBOs, for fault protection and, AFAIAA, very few (if any - I'm never seen one) of them will have FEs.
Kind Regards, John