Well it tells you everything you need know about Ireland from 400 to 1200. Pretty easy to read, lots of smaller sections and chapters. It's academic a bit, lots of references and further reading an bibliography, but it's not dry. Covers lots of topic, Irish law, church, St Patrick, Vikings, High Kings etc. Its a bit long.
If you wanna know about this period of Irish history (or a part of it), this seems like a good book. Otherwise, maybe give it a miss ☺