We've been running the numbers for a quartz worktop for a kitchen renovation. Running it through diy-kitchens.co.uk we got a price that was about £400 cheaper than estimates from Benchmarx, Magnet, a local kitchen shop (high end), and almost £1k cheaper than Wickes(!!).
The total predicted by diy-kitchens is £2.5k and other local kitchen shops are quoting £2.9k (Wickes quoted £3.4k but I have no idea what was up with that!).
My feeling is that many of the above people are going through the same supplier. Still, the DIY-Kitchen quotation is so much cheaper that it's hard not to be suspicious.
Have any of you used DIY-kitchens for quartz worktops?