These short guides are both really helpful and difficult to write and write about. They assume some, but not too much familiarity with a subject. If you have no understanding, they probably are too advanced. And if you have a lot of understanding, these types of books probably will not be all that interesting.
Mostly I picked this up because it was on sale and because I wanted to read Barclay’s Paul and the Gift, which yet again I heard some bible/theologian people on twitter talking about as one of the best books of theology of the past decade or so. (It is also on sale for Kindle and even a better deal at less than a penny a page.) I have a pretty good understanding of Paul, I read NT Wright’s biography of Paul fairly recently and I have read a number of other books as well. I thought this would help introduce me to how Barclay thought about Paul, and I think it did a bit.
It is short, less than 100 pages and in that short page span, Barclay gives a brief bio, a discussion of what books he likely wrote, and how Paul influenced later Christian history, especially Augustine and the reformers. That is a lot to cover.
If I had to recommend a single book on Paul to a layperson, this would be on the list of books that I would consider, but I would probably rank Wright’s higher because I think it was more thorough to introduce the many issues of Paul. This one is certainly a good short intro, but maybe too short for many.