Review on Elevate your Raspberry Pi Cluster: Eau 4-Slot Stackable Case for Raspberry Pi 4 and 3B+/3/2 Model B – Clear Acrylic Case with Cooling Fan and 4 Layers Pi Rack by Lynn Woodcock

Easy assembly. The set I received was mislabeled. I mixed up the screws for the fan with the screws for the IP. Eventually one of the acrylics broke before I realized the mistake. The nuts go into the fan. But the way it's set up, I could get the fan to blow onto the top of the board. If you build it exactly like the product photo, the bottom Pi doesn't get a fan, and the top fan just blows air from the top.