I haven't used it, but the previous owner of my house used their mail redirection service, and it didn't work, we still got most if not all of their mail. I'd think the minder works on the same general principle.
Mailminder is a service whereby An Post will hold your post at your local delivery post-office while you are on holidays etc. There is a charge for it, and as far as I remember it doesn't come cheap. However, if you do not want anybody coming to your house your choices are limited - either have it delivered or pay for the mailminder service. It usually works okay but can fail if/when your local postman/postwoman goes off sick or on holidays and the stand-in is not aware of the mailminder instruction.
Used the redirection service last year when i moved to snag any mail i did not do a change of address.
Did not start on time even though i signed up in time. Had to go into them to address this.
Sporadically worked then and when it did not work for Xmas post I complained and got my money back.
The redirection is an Unreliable service and i would have been better off giving the 95 euro to the people who bought my house as they were the ones who gave me back my mail!