Four Pi 4s, a stack of little acrylic plates, a cheap eight-port switch and a USB power supply that I am fairly sure is not rated for this. The plan was to "learn Kubernetes properly". The reality was a delightful afternoon of cable ties and a weekend of kubeadm swearing.
Here is the honest assessment. I learned nothing about Kubernetes that I could not have learned faster from a single-node kind cluster on my laptop. The networking on Arm with limited RAM mostly taught me about the failure modes of cheap SD cards, which is a real lesson, just not the one I signed up for.
And yet. There is something about physical nodes you can point at, with blinking lights and a fan you can hear spin up under load, that a VM will never give you. When I kubectl drain a node and watch the pods shuffle onto the others, then physically yank its power and watch it cope, the abstraction becomes a thing on my desk rather than a diagram.
So: not useful, in any way I could put on a CV. Enormously good fun, in every way that actually keeps me doing this for a living. Sometimes that is the entire point, and I refuse to apologise for it.