Bought lots of components off them over the years, but never a complete PC because I've been building my own for about 20 years. It's only recently that commercial PC builders have begun to understand the peculiar needs of DAWs.
My experience has always been positive, including the time a few years ago someone put three RAM sticks in a package instead of four. Problem was sorted out very quickly.
Having said that, I've not been entirely convinced by Scan's choice of some components when I looked at their DAW PCs two years ago. Particularly regarding cooling and cases - my experience has been that for minimum fan and other noise Noctua take some beating. The PC in my sig has only two fans, both Noctua 140mm running on reduced voltage, one on a big Noctua cpu cooler and the other extracting air from the back. It's nearly inaudible from six feet way in a quiet room.
I doubt there's anyone in the UK doing a better job though, at least not at those prices. Quiet PC are also worth taking a look at for components and builds and it's always worth checking what the components in a ready-built PC would cost if you assembled it yourself.