I purchased 5, 6, 8, 10, and 14mm CMT cutters from Amazon after buying a Domino XL. The 14mm broke on the second cut, as I posted earlier. The replacement cut a series of 6 inch long 40mm deep mortises in hard maple, however, and is still going strong. Last night I make a test block out of a scrap of oak newel post using all my cutters in both standard and the wider width. I am happy to report all the cutters worked fine. I plunged the XL cutters to 40mm and the little ones to 25mm.
So I think my experience with the first 14mm cutter was just a bad bit, something that happens, especially with really hard metal. Hard has a strong tendency to mean brittle so it only takes a small unnoticed crack and the tip breaks off.