My Montessori book (Teaching Montessori in the Home: The Pre-School Years) suggests using geometric insets to help with coordination and learning the names of shapes. We have some shapes puzzles, but I decided to make some insets anyway because they seemed pretty simple and I had some stuff lying around.
It was very easy to cut the yellow shapes, but much harder to cut the blue card stock to exactly match (even with the tracing). I especially had trouble with that rounded cross or x-shaped one. (What would you call that? And why is that shape one of the six? I could think of a lot of other shapes that would be more common.) I'm sure we'll use them a bit, but I think you might do just as well with puzzles without all the hassle.