Thanks for the replies guys - it sounded like a stupid question when I typed it.
I think the main benefit for me would be for hard floors, which I plan on expanding into in a bigger way next year, as others have mentioned I can't see much use for it with carpets at present, but I stand to be corrected.
I can get a good condition Numatic with a tank for £200, including drive board and brush.
Like the look of John's package deal, but I've just bought the new Airflex, I need to upgrade the van and a new cfr tool is a priority as my drimaster is showing it's age.