I have one, and yeah it's usable.. but I don't use it as my main PC mostly because I like my Windows setup on my other machine better. But if I had to, I could definitely use the KDE desktop.. I've already spent awhile making it look nice. Windows drivers for it are missing important functionality so I wouldn't bother looking to run Windows on it. The desktop is also missing bits and pieces of functionality, e.g. no printer system is present.
The way they have set it up, it has two environments. Both are immutable. Gaming mode which is Wayland and Valve's own setup like a console, and desktop mode which is X11 x.org using the KDE desktop which can only install new apps from flatpak.