Hi, Unfortunately, we don't yet have any experience with these solutions.
However, I did begin looking at the topic a few weeks ago and here's my two penn'orth:
These small PCs are commonly known as NUCs - which stands for Next Unit of Computing.
Some manufacturers, such as Intel, have spotted the market opportunity in IP CCTV / surveillance software and have covered the topic at their website:
Intel® NUC Digital Security and Video Surveillance Solutions
Likewise, some specialist NUC resellers:
Go Small, get Big
(Actually, when you click through on either of those search results you get a 404 error page at the moment, but they may be worth calling for a chat on their experience with NUCs for this application).
A general IT reseller such as Scan or eBuyer might offer lower product purchase costs?
https://www.scan.co.uk/search?q=nuc
Cheap Barebones PCs Low Prices UK Deals | Ebuyer.com
Finally, I began my search due to dissatisfaction recently with NVR developments and performance.
I suspect that software on a suitable PC could deliver a more satisfying solution.
However, my quick conclusion was that, due to the relatively high cost of these NUCs, most people would still prefer a more cost-effective and dedicated NVR box.
NUCs are typically provided with the Windows Operating System.
Adding FREE surveillance software is probably key to keeping costs at a level where it's worthy of consideration.
Hikvision's iVMS is probably THE most obvious.
But,
Vivotek's VAST 2 software used with their IP cameras is definitely worth consideration, as many customers have praised that software.
Perhaps GeoVision's cameras and software are worth considering too.
A minimal cost solution may be possible by loading Linux onto an NUC and then using ZoneMinder as the VMS software.
Footnote - most people will also want to be able to see home from their mobile phone, if you need that capability then make sure that a suitable App can be added.