We have mixed experience with Au Pairs.
We tried one ourselves but it didnt work out, Amelia our Daughter didnt take to her, it turned out she had very little experience with kids and it showed.
How ever my wife Sarah’s sisters all have Au Pairs and they are brill with the kids fit in to the family life very easily.
Its not for everyone you are opening your house up to another person so you do need space so that everyone is comfortable living together.
There are saving to be made compaired to childminders but its not for everyone.
I can find out what agency we used but I know that most of the Drogheda based Au Pairs go the Edgewater College for english classes.
Good luck with it.