The ethnicity estimates are to be taken with a pinch of salt- they occasionally get updated and parts you had disappear or new ones reappear... and different sites will say different things. As far as matches go, sometimes they have trees and are responsive, other times they don't have trees and don't respond. It takes time to go through the information presented and for the most part I've been happy to confirm the paperwork through shared matches. When it comes to illegitimate ancestors, I had a suspicion about the father of one (and I have a whole mass of matches on his side of the family) and no information relating to the father of another (but by cross matching shared matches of his descendants and eliminating ones proved to be from the 'wrong' branches, I ended up with an unknown family that I'm quietly confident is the unnamed father's family).
If you are interested in Ireland, it would depend on how far back your Irish connection is- too far back from present day and you may have a slim chance of matching with legitimate cousins / cousins may not have information back far enough to connect on paper- but in theory you might end up with the same surnames and places as other people and start to put together puzzle pieces.