I don't know who needs to hear this, but I couldn't find any useful information about it, so I'm writing it down: yes, the Microsoft Xbox One TV tuner works as a Plex DVR tuner — with caveats.
It's a USB DVB-T/T2 stick that Plex recognises on supported systems. Signal quality matters more than with a TV's built-in tuner, so use a proper aerial feed, scan patiently, and don't judge it on the first pass.
One of those notes-to-self that might save someone else an evening. Normal web design and SEO service resumes shortly.