I don't have any experience with the Irish system, but that's the way it works in the US. You don't need any special permits, or need to send more than one bag, if that's what you're wondering.

When I worked at a university in the US, we used to encourage foreign students to use that method if they had a lot of books they wanted to send home.

There was a certain professor who edited a journal that was printed somewhere in Europe—I don't remember which country. For each issue, he received a certain number of copies to distribute himself; they arrived by M-bag. I think it's an international system that's supposed to have uniform rules. Of course, each country will set its own rates.

The USPS web site is likely to have more detailed information than the web sites of other countries. See here. The web site doesn't specifically say that the rules are the same everywhere, but I think that was the intent when the system was set up.