I have acquired two new 9FSs in the past two weeks. I spent a lot of time researching folders and the Downtubes seemed to be the best bang for the buck. Now that I have had them and ridden them I can say that I am very pleased with the choice. Great value.
The one feature that is missing, in my view, is mechanical "keying" of the handle bar stem to the base tube. Every time I adjusted the handle bar height it took me several tries to get the bars perfectly square to the front wheel.
The Dahon folders have a design feature for doing this. I decided to add a few small parts to achieve this function on my DT. I have installed this mod on both bikes and it is working very well.
If you are curious, I have posted a small group of photos of the mod on my photography site. This will take you straight to the gallery, or you can get there from my website, imagesbypyarnall under "Pages". http://www.imagesbypyarnall.com/ibpy.../downtubestem/
Contact me if you would like more details. I now consider it an added layer of safety in case the clamp is accidentally released while riding, though that seems admittedly unlikely.