Worth reading because it challenges old assumptions, as basic as the assumption that the Dal Riata Scots came from Ireland, and it tells well how use of names for people groups started, how it was often indiscriminate and not accurately confined to descent groups, and how it was this way that the country ended up with its present name but really we are descended from all the previous peoples here right back to the stone age.
It's not a history of Celtic conquest and replacement, Celt was a generic term we got included in, and Pict was a sort of national descriptive name first used by the Romans to describe a certain collection of tribes including the Caledonii. So the Picts were us all the time. The old small kingdoms were not nations they were in constant flux and innumerable, many of them we have no record of, some named ones don't know where they were even including Rheged, adequacy of evidence for locating it around the Solway is challenged. It makes Scotland feel far more continuous and soldily grounded than did the perception of these as separate people groups. Valuable to learn that the Strathclyde Britons were not Welsh they just spoke it, because language all over Britain went P-Celtic i.e. old Welsh, except around parts of the Scottish west that were isolated landward by mountains and had more contact with Ireland so adopted Gaelic. Scot started as a Roman term for Gaelic speakers around Argyll, "Picts and Scots" represented a language divide, and eventually the name Scot simply prevailed over Pict because the Gaelic culture was more socially advantageous at the time when the culture of small kingdoms was ending and all the king lines blending.
It's good to have the gaps in known history and the unreliability of sources declared clearly and honestly. Wish he had felt less need to make up for it with too frequent descriptions of "perhaps" and "likely". It was frustrating reading the history of the small kingdoms period, too chaotic a narrative to keep track of for writer or reader, and is all focussed on the south, mischievously he calls the Picts of Moray "Moravians!" and he says very little else about the north highlands' history, it is not always kept clear when Bernicia was functioning as a kingdom, and all this does not lead anywhere, as the key figure of Kenneth MacAlpin just appears arbitrarily out of the unknown. And after all that effort, he hardly mentions the Battle of Carham and does not describe at all the emergence of the Tweed border. He does not describe fully the Strathclyde kingdom's ending, how it became a client throne then was abolished. In fact, after reading all that unfollowable toing and froing of the small kingdoms, the ending is rushed and an anticlimax, and lets you down in relation to prominent formative events.
Curious mixture of valuable new challenging insight on the earlier period and total letdown on the period of the Scottish state's emergence.