http://www.scan.co.uk/3xs/custom/steammachines/form-factors#anc
The specs are a bit limited, there's no option for any AMD GPUs (it's the same for all their custom builds albeit), and £950 seems a bit sharp for a small form factor 6600 + 970 build with a 8GB of RAM a 500W PSU, 1TB HDD and 240GB SSD when building a PC of the same spec would cost £830 or thereabouts, taking into account the steam controller that comes with it, but for those wanting a more hassle free "plug and play" experience and a 3 year warranty for the whole system, so they don't have to get too involved in the "nerdier" side, it might be an attractive option. The first year of the warranty includes onsite support, and SCAN also do hardware upgrades on GPUs and CPUs, and add storage if it's under warranty - providing you pay postage and for the parts.
This is the first time I've seen steam OS offered up like this. It's a pretty good console replacement for those reluctant to get their hands dirty with the building and possibly repair side of things themselves for at least 3 years I suppose.
Whether it's worth £120 or not is up to them, though. It does seem a touch on the steep side. If it were in the double digits, I think it'd be more reasonable. For £120 I'd expect their better warranty to be standard, or at least including the CPU overclocking service, motherboard upgrade service and storage replacement (for swapping out still functional drives).