The book is broken up into four sections. The first (1607-1660) discusses mostly how Scots migrated to mainland Europe and Ireland rather than America and served as mercenary soldiers. Also, Scots lived, albeit in small numbers, in colonies controlled by other European nations, like the Dutch and Swedes. He provides numerous examples of trans-Atlantic trade by Scottish ships to debunk the myth that Scots didn't set up their own colonies because they were inexperienced sailors.
Parts two through four cover information from 1660 to 1785 and are broken down by region (New England, Chesapeake, Canada, West Indies, Carolinas, etc.). The divisions are somewhat arbitrary with New York getting its own section in one chapter but being lumped in with the Mid-Atlantic colonies in another. Some of the stories and people he refers to are brought up in more than one section. He might have been a bit more successful focusing on a specific region all at once and then moving on to another.
The book is clearly well researched, but doesn't get bogged down in statistics. He makes a generalization (ex. that many Scottish tutors moved to the Chesapeake region), provides a few examples and then moves on. Some of the generalizations and statements get a bit repetitive, however... like how many Scottish merchants there were or how criminals were transported to the colonies.
Overall, this is a good introductory source for anyone doing research on their Scottish family history. You might catch an example of a family member used as one of his examples, but you would have to go to his sources to find more detailed information. Dobson is the author of numerous directories of data, which focus on specific regions, so that would be where one should look for more detailed information.