I did a simple review on my Dahon Jack; it is on the Folding Society website:
I have ridden some more MTB trails on this bike since I wrote the review, and I have changed my opinion, slightly. I think it is fine for less-technical MTB trails. I still rarely take it on very technical trails, because really (to survive on them) you need: a. Very strong brakes, like disc brakes, and b. Shocks to absorb the blow
I know, I am going to open a can of worms with this: "Oh, so you can't ride a rigid on technical trails, eh, wuss?"
Hey, you do what you like. I rode this bike on three fairly technical trails (Ferdinand Forestry, in Indiana, Waverly Park, in Louisville, KY, and Shakertown, KY). I crashed at Ferdinand, and busted my face up; not because the bike's folding mechanism failed, or the bike failed; I simply did not have the stopping power I needed on a steep hill.
At Waverly, I was fine, but I had to slow down a lot, I didn't have the clearance for the many large logs, I rode the V-brakes all the way down some hills, with squealy pigs behind me, and I had a tough time climbing any really steep hills. At Shakertown, I had a great day, but had to dismount on some tough rock gardens and also suffered clearance problems on logs. My regular MTB has high clearance and 110mm shocks.
I have gone to many cities and been able to easily take the Jack with me, and enjoy lots of trails. I mounted some Panaracer Fire XC tires, and I was all over some easier rolling trails. I have found that the best solution for me was some dual-purpose hybrid tires, with knobs, but also with a rolling area. That way, I can ride on the road, while traveling, like a few weeks ago in Nashville, and I can also ride on rolling trails, like Capitol View Park in Frankfort, KY, or Veteran's Park, In Lexington, KY.
That's what I wanted the bike for: traveling, and I also ride it to work sometimes. I can fold it under my desk at work, and it stays safe under there all day.