I have tested with both Ancestry and FTDNA. I found more of the matches on FTDNA replied to my emails.
I was pleased that the resulting matches confirmed the paperwork I had done on 3 of my 4 four grandparental lines (the fourth -Murphy from Cork I have postponed doing serious research on). The DNA matches confirmed the work we had done on an illegitimate daughter of a great aunt, who had been fostered out away from the family. The matches also led to contact with the descendants of three of the family who had gone to Chicago in the late 19th century. It meant that we from Ireland were able to put those Chicago relations back in touch with each other too.
So to date DNA has served more as a confirmation of existing paper-based genealogy. However I hope in time it will lead us to my father’s half sibling, born in England somewhere in the late 1920s or early 1930s, of an Irish mother, and my English grandfather William Edward Williams. Whilst we know my grandfather continued to support the mother and child after he returned to his wife and children in Cork, we do not even know whether the child was a boy or a girl.
To date we have had nothing useful from the Y-DNA testing done in the family.