The books are workbook in format, but carefully make use of (and include explanations of) the Montessori philosophy throughout.
The kit includes workbooks, answer guides and manipulatives for grades K-4. The manipulatives are quite nice for "inexpensive" products (in comparison with those you can purchase for starting up a Montessori school). The bulk of the expense of the kit is for the books. Some of the manipulatives are inexpensive and readily available at teacher supply stores, where others are custom made for Schiller, like the "numbers bank", a lovely set of numbers in a wooden box (with sliding lid) that helps teach place value (my kids have really enjoyed using this!).
Scripted programs are not for everyone. They tell you exactly what to say at each point, which are helpful for some parents and annoying to others.
The best way to more thoroughly understand the program offered here is to visit their website where you can view pdfs of all the materials included, sample pages and more: SchillerMath.com
While this particular kit is intended for grades K-3, Schiller also has Math materials available for grades 4-7.
The K-3 kit is quite expensive (about $500), but includes a large box of books and materials (including a CD of math songs to accompany the program), plus 5 years of free downloads of consumables - to cover younger siblings. Keep an eye on their website for discounts and sales which seem to come up frequently.