It’s got a sturdy binding, and it does a decent job of clearly and accurately defining a circle, providing lots of color photos of real-world examples, with the circles brightly highlighted.  The examples are ones small children will easily recognize:  wheels on a car, pizza, hula-hoops, etc. But really, how much is there to say about circles?  It seems a bit pricey to spend over $100 and invest the shelf space to buy 6 different books to describe 6 different shapes.  If you’ve got the room and the dough, this series at least doesn’t seem to erroneously include incorrect examples (including spheres with circles, for example).  What I would be particularly curious to know is whether the rectangle book includes squares, as it should, and whether the hexagon and triangle books are careful to include non-regular shapes.