I want to uninstall PureOS and install a different OS, do I need to uninstall the factory installed Pureboot bundle and re-flash the firmware?
Or can I just throw the Librem key and vault USB sticks in the back of the wardrobe and just reformat the boot drive and install my new OS?
You should be able to use Pureboot with a different OS if you want. I confirm it works with Qubes OS.