The value of this book lies in its bringing together a number of drawings of Celtic Crosses - as additions to market cross, as free standing crosses, as illustrations within a paten ... etc. And the author calls attention to details within the crosses that might otherwise be overlooked.
However, if you are looking for a book to interpret the crosses, one can better spend one's time looking for better sources. Bryce feels comfortable asserting that early Christianity was estoteric (the Gnostic Christianity was), asserting that Hindu worldviews are imbedded in the Celtic symbolism (they are both IndoEuropean there could be a connection), and otherwise assuming that "universal" can be assumed - it doesn't require proof. By the end, I was unwilling to trust anything the author wrote beyond the dates, locations and other basis information associated with the crosses. On too many points I wanted to steer him to reliable sources such as Pelikan on the history of images of Christ to modify his over simplification.
Nonetheless, the book is worth its cost for the illustrations - and some of what the author writes is useful.