This is an excellent product! I ordered it for my 17 yr old son, who plans to be an engineer. I wanted one that was both challenging, yet reasonable. This fit the bill perfectly. He is even now sitting and diligently working on it. He's been at it for about three hours now and almost done. The one negative thus far is that the holes for the toothpick were a bit tight so he employed pliers to help. I love how absorbed he is! I will be buying these again- soon