I bought a couple of these
They call these the Heatsink Case. These cases are basically 2 pieces of anodised aluminium, some thermal pads and 4 screws. They are also available in a gold colour. With an ambient temperature of 25 degrees C they hover around 67 degrees when crunching so they help but are not as good as a fan case.
Having done the cases, both of these Pi4 4GB have been added to the cluster until the Pi^4 cases are sorted out. That brings Marks Rpi Cluster up to:
3 x Pi4 8GB
2 x Pi4 4GB
6 x Pi3
2 x Pi4 2GB support nodes
In other news the Raspberry Pi Foundation upgraded the kernel from 5.4 to 5.10 which has only recently been released. Debian haven't even got their 5.10 kernel out of testing yet.
The Rosetta app doesn't like being stopped and started which means I have to run each machine down so it has no work on board before upgrading it.