Your way is less of a nail-biter for sure. One other possiblity is refurb SFF office pcs, though considerably larger than NUC/set-top box, you can get a pretty powerful rig for less than half what you'd pay for the latest model @ retail. Also they generally have Win10 Pro license on board.

I've been doing just that, our place went through a cull on desktop machines and replaced them with laptops so I've been able to liberate 4 SFF HP boxes from the great scrap pile in the sky with i5s and at least 8GB RAM TBH in each. 

Found a nice bonus in one, a spare 1TB HDD.

And dust. So much dust. 

Those old HP boxes never say die! Dirt cheap, tough as nails, and surprisingly powerful considering the first part.

Ended up getting a PN51 direct from Asus 32gb RAM, 1Tb SSD.

Should keep me quiet for a while.

Installed Forza Horizon 4 Ultimate for a giggle, actually runs fine, admittedly not in full fat settings but I can't tell the difference in graphics nor performance against my Xbox Series X, which is nice.

:)

Looks very nice. I built a tiny PC to dump all my music CDs onto 42301.1 based around an ASRock STX motherboard. I imagine it's about the same size and, in the end, probably cost me almost as much as the much-more-powerful thing you've got. It was fun, and it did have space for the 2 SATA drives I wanted (along with an NVME drive), but I'd probably have been better going for something ready-made.

Looks a nice little system, hope it does the trick! Back when I bought my NUC, Ryzen systems were pretty much an impossibility to find unfortunately, still for a torrent machine, it does pretty well.

So far - so good (yes)

On the back of this, I'm upscaling my Alienware with a 1Tb SSD in place of it's current 1Tb HDD.

Presumably I can just take out the HDD, insert SSD and then install Windows using the USB thingy that I got from Dell for clean/re-installing/repairing Windows 10?

Yep, should work fine. And of course if anything goes wrong, you can always pop the HDD back in temporarily to resurrect the system.