Let me begin by saying that I did not buy this toy from Amazon, but it really doesn't matter about that.
On the surface, this looks like a really nice building toy, some combination of classic k'nex and building blocks similar to the lego style. However, my kids soon discovered that the blocks just do not stay together. It's basically impossible to build the bulldozer with the rubber belts around the wheels because the belt just keeps pulling off the axles from the main body of the machine. They just won't stay on. The other blocks do not stay together either. The traditional k'nex pieces of the rods and the spokes work great, but for the blocks, stick with Legos.