The Amazon listing for this is a real mess. The title/description appears to list 6 titles as being included in this 3 volume boxed set. Some of these are obviously duplicates of each other, others less obviously so. This is a bit confusing to the newcomer to these titles, particularly as there is apparently also a fourth title in the series.
The Amazon reviews are culled from reviews of the individual volumes as originally (separately) posted. While this is understandable, it leads to confusion when a reviewer compares "this volume" (which one??) with "the other volumes".
The listing also tells us that customers who bought this boxed set also bought the individual volumes. Really?
By the way, potential purchasers might like to note that (at the prices at the time of writing) you save 3 quid by buying the individual volumes separately - at least I think you do, but that of course depends if I've correctly understood what's actually for sale here...