An A4-SFX v2 case (or a similarly sized horizontal PC if you prefer that) is a much better console replacement IMO. At only around 7L, it's about the same size as the original X-Boner, and you can fit a full size GPU and just about any CPU you want save for Threadripper/Core i9 (due to space constraints with the CPU cooler), and upgradability is almost on par with a full size tower (though you can't do SLI)
That's more of a "console replacement for those who want the power of a gaming PC" though, as the case isn't exactly cheap, so it's not really worth putting low end components in it unless you just have some laying around and are planning to upgrade in the near future.
There's something to be said for that upgradability though, which is something all of these ultra small prebuilt PCs lack. And those NUCs aren't exactly cheap either.
And if size is the primary concern, there are lots of ultra small prebuilt PCs with far better specs than this, some even have a GTX 1080 in them, although they are expensive due to the MXM form factor coming with a high price premium for high end GPUs compared to PCI-e.
first i've seen size/weight or whatever being measured in litres
It's becoming a pretty common thing in the SFF market, it's much easier to see at a glance how two different PCs compare in size, especially if they're different form factors.