wrenches

Hi all. I'm thinking of investing in one of these sets or maybe just the two tools separately, the thing is I have no experience of impact wrenches other than what I have read spec wise. I know that 10.8 volt is a little lightweight but the kit would only be for small scale DIY / non ferrous...

Has anyone here purchased and used one of these 12v impact wrenches and are they worth it ? Seems like a good gadget but then, how often would you use it ? http://www.autoexpress.co.uk/products/products/217677/impact_wrench_test.html