Consul and Vault offer functionality that Kubernetes is completely lacking, though.

Is it worth going with those? I'm torn between deploying stuff on Kubernetes (on a managed control plane, of course, which you can get for free nowadays with providers as long as you use their own machines) and rolling my own with the Hashistack.

Depends on your use-case, really. IMO, Hashistack is fine if you have well-defined requirements. You can pick and choose the components you need (including non Hashi stuff) and integrate them with relative ease, keeping resource footprint and operational complexity at a minimum. I’ve found that it’s quite easy to pinpoint problems when they arise.

Kubernetes is more of an everything-and-the-kitchen-sink approach that you can’t really outgrow but because of its monolithic design, debugging can be quite challenging. It does, however, come with a much larger and much more active community that you can go to for help.