I bought my IXFS off ebay.co.uk (search for seller "downtube1") for £180 + £35 or so VAT and £25 postage. No import charges as the bikes are already in the country - Downtube have some sort of depot in Folkestone and sell all their UK bikes through ebay. £180 seems about the going rate for IXFSs (though some have gone up to above £200); about £150-160 for the other Downtube models. At that price, it is hard to make a case for buying anything else (unless you have money to burn).

Everything was very easy - couriered to by FedEx, arrived with me in two days. It needs a bit of set up on arrival, probably best done by a shop unless you're the sort of person who likes adjusting, lubing and all that stuff. Despite a tune up by my LBS, the gears were still a bit off, but a quick email to Yan at Downtube and subsequent phone call sorted the problem out (the LBS hadn't properly tensioned the cable) and the bike now rides very nicely indeed. Customer service at Downtube can certainly be recommended!

Have now ridden it a fair bit and very pleased with my purchase. The only kit I've added are lights and a Topeak EX beam rack http://www.topeak.com/2006/products/...beamrackex.php. for £25. It doesn't fold as small or as neatly as a Brompton (not much does) - rather than a small neat package what you get is a bike folded in half, with flipped down handlebars. And unless you tie it up with bungees, it doesn't stay as one tidy package. But the Downtube is cheaper, has more gears, bigger wheels, and is eminently luggable - I've taken on the bus folded up with no problems. And getting it into a car boot would be problem free.

Your choice of Downtube will need to reflect your size and intended use. The IXFS is the heaviest, but can capably accomodate my 6'2" frame. The front suspension and no suspension bikes are apparently less well suited to tall riders, but are cheaper, a bit lighter, less bulky and have a fixed rack at the back, so no need to mess around with fixing on a beam rack.
y
One thing about the Downtubes (particularly the FS) is that they look fairly startling by UK folding bike standards. I guess if you want that Brompton look you could always go for a Merc - essentially a Brompton clone, sold with lots of accessories. The pros and cons of them are well explored elsewhere on this forum. There is a new 3 speed Merc on ebay.co.uk at the moment for £330.

Best of luck, whatever you decide to buy.