I have four fixies (two actual track* bikes, one 700c conversion and a Moulton TSR, which was crying out to be a fixie and is all the better for it).
I wouldn't ride the Dunwich Dynamo on gears now. Done it three times on fixed. Gets easier every time. Like going for a long walk.
It doesn't suit the type of racing whippet with little dinosaur arms. You have to wrestle the bike up hills and stand on the pedals a lot to save your knees. You cannot control cadence, only torque. This is not a bad thing. The human body is capable of doing a lot more than cranking out constant power at 90rpm. Leave that to the machines.
*once you're used to the toe overlap and the skippiness of the rear wheel over bumps, a track bike is a delight on the road. Track forks are stiff in all directions (round blades, not oval) which is great for honking up hill, and it's as light as a bike can be