So let's say you want a folding fixed gear. What are your options? Well, so far as I know, only one is made stock. Why would you trouble yourself?
- taking on transit and travel
- keeping it safe inside at home, work and play, without a heavy and unreliable lock
- fewer parts to buy or maintain
- the pleasure of fixed riding
You could take a Dahon Mu Uno and have the rear wheel rebuilt and some brakes put on*, but I don't think the quality is worth the trouble, especially as it is too small for me, a 6'er.
You could just buy the Montague Boston, which is ready to ride as a fixed, though it does not fold small, and fenders would be a PITA.** Two sizes, so not too small.
You could do something with a Brompton or a Moulton, but if you have the money for one of those conversions, you pay people to do it for you, not read blogs for information. You could deal with Bike Friday's execrable website, and negotiate with them for a build, but that's a pain, isn't it? Last I heard you're looking at about $1200US for the fixie, which is not terrible, but Bike Friday's prices always seem about 20% higher than makes any sense. BF does have many sizes, which is ideal.
A far more reasonable option is the Swift Folder, which doesn't seem to focus so much on selling their own anymore, but have licensed to Xootr. Xootr sells a singlespeed for $700, but it is not 'fixable', so you're going to spend another $200 on a hub and wheel rebuild, and larger chainring. You may be best off going $500 for the frame and basic parts, and spend the extra money on just the build you want. Xootr is aluminum, as are the rest, but it is possible to get the Swift in steel, if you think the ride will be better. Not sure if it matters in this design. Various sources of Swift sell it in several sizes. You can have a build made at either of these two.
My idea? Bike Friday or Swift fixed, possibly with drop, track, bullhorn or Friday's H-bars. Yes, fenders too. If I am feeling eccentric, get it built with a Sturmey-Archer S3X!
*If you think you can skid-stop with a 700c wheel, you're an optimist; if you think you can with 20" wheels, you're... SMACK!
**I like fenders and brakes: yes I am old, but I am uninjured and I am dry.