The title and the date of the book drew my attention immediately.
Set around the time of my own writing it's interesting to get the perspective of other authors. The intention of this short prologue is to introduce the books which follow. Will go on and buy them? Yes, I probably will because I don't personally focus on the spiritual aspects of the druids but I think I'll enjoy what Ian Hall brings to his novels regarding the functions and special powers of the druids in the lives of the Late Iron age peoples of northern Britannia.
(If he has any particular verified ancient sources to share on this aspect of druidism I'd be delighted to read them!)
There are quite a lot of historical themes in this short introduction which display a good knowledge of the era.
The link with the sons of Venutius, King of the Brigantes is an interesting one.