This product is a bit problematic to review. At one level the adventure contained inside is workable as such and I might perhaps use it some day, on the other hand adventure material and production quality is not up to level with Guild Companions Publications quality in modern times.
The motivation of the product was as far as I understand to promote the excellent Construct Companion from Guild Companions Publications, unfortunately The Toyman's Fair is written to be standalone from the Construct Companion. The downside of this is that the result become rather dull. If you have Construct Companion it would take little effort to produce a more interesting adventure that makes use of the many more options contained in Construct Companion. Without Construct Companion the Toyman's Fair makes less sense since the adventure lose much of the point if you don't have access to the rules to crate the challenges in this book.
To sum it up, this product has some good points but it suffers from the tries to make it standalone from Construct Companion. Purchase it if you want to support Guild Companion Publications, but if you have limited funds many of the other Guild Companion Publications products are better choices.