This toy is awesome - if you want to call it a toy. I prefer to call it hands-on physics and engineering, which it undeniably is, as your child is physically dealing with gears and pulleys, wheels and axles, and all manner of mechanics as they build working models of various machinery.
My 11 and 13 year old sons were enthralled from the minute they opened the box. They couldn't wait to finish one model so that they could build the next. They asked me which one I wanted them to build first, so they made a hand blender, then after my "oohs" and "aahs", they quickly decided on the centrifuge ride and then on to the garage door. There are also instructions for a sewing machine, transmission, mechanical lift and a host of others included in over 24 models. The instruction guide is easy to follow and requires no reading. This set also includes a Curriculum Guide Teacher's Manual with Student Activities if you want to go even further with learning about how each invention works and what else can be done with it (such as modifying the machine to make it work faster, etc.). My 13 year old just finished making the mechanical lift and learned about "thread and pitch" from the Curriculum Guide.
If your child has a definite bent towards mechanics or would just like to learn more about machines and loves to make things, then Fischertechnik from Timberdoodle would be well worth your investment. When weighed against something like Legos pricewise, the price for this Universal Set with 24 Models is comparable, but the learning value of the Fischertechnik goes way beyond its price.