The manufacturer of BIRDY folding bikes (Riese und Muller) has announced new bikes, with new Frame Design. This bikes will be available on november 1st in Germany, and later in other countries (I hope I can buy a frame kit).
I have a Birdy Grey (Black Edition) with Rohloff internal hub (14 speeds) for a total of EUR 3000 (USD3000-USD3500), and this bike drives really well (actually I drove 600 km to Paris with it this summer). You can get also a Low Rider and Expedition Rear Rack. I could everyone recommend to evaluate this bike if you consider buying a serious folding bike.
Here are my opinions:
* In my opinion the Birdy looks much more robust than any Dahon bike (if you see both bikes in real life, on internet they both look nice). E.g. The extremely oversized main frame (Birdy current model) looks more impressive than the Dahon frames. Dahon looks more fragile too me (but this result in nice specs (weight etc)). Also the top line of Birdy comes with Deore XT where Dahon ends up with relatively cheap SRAM stuff (e.g. Dahon Jetstream XP).
* Drives extremely well;
* Rohloff internal hub works extremely well (a bit noisy the first 1000 km);
* Extremely stiff frame (new frame is even stiffer according to R-M), because no folding point in main frame;
* Nice options available (low rider, expedition rack).
* Rohloff chaintensioner adds some resistance (i am not sure this is more than a derailleur as chain 'tensioner').
* More bulky than Bromptom;
* More expensive than lets say Dahon;
* Maybe unusual 18 inch tires.
For a nice 'interactive' view of the bike see here:
Flash demo at Riese und Muller website