Hi Ramon. I don't live in Boston (or even in the U.S.A.), and I don't own a Downtube 8FH. However, I do own a Downtube Mini, which I have owned for less than a month, and 2 Dahons (Curve SL and Jetstream P8), which I have had for more than a year. In my experience, the Dahons are way above the Downtube in quality, fit and finish. I'm afraid that if you already own a Dahon, you might be disappointed with a Downtube. I know I am.
The seatpost on my Downtube bent on my first ride (35 km ride, and I am 5'9''and weigh 170lbs). I had problems getting the Sturmey Archer 8spd hub to shift properly right from the beginning. After about a week, it died altogether. An internal spring broke, and it's stuck in first gear. I called Yan about the seatpost, and he mailed me another one, which arrived yesterday. It's exactly the same as the one that bent, so I'm sure it will too. Tomorrow I'm going to a metal shop to buy a piece of aluminum rod 7/8" in diameter by 17.5" long to install inside the seat tube to keep it from bending.
I called Yan a second time about the defective hub, and he said he'd send me a replacement, which I am still waiting for. I e-mailed him and asked if he was sending an entire rear wheel and hub, or just the hub. He said he's just sending me the hub and shifter, so I'll have to pay my LBS to swap out the hub on my rear wheel. Needless to say, I'm not impressed.
The Dahon Curve SL has a Nexus 8spd hub, which has performed flawlessly from day one. It also came with fenders and Ergon grips. The Downtube came with crappy rubber grips which I immediately cut off, and replaced with Ergons. I also installed a set of fenders and upgraded the seat and pedals. The brakes and brake levers on the Downtube are no-name, and look it. I'll probably replace them this winter. I'm even contemplating replacing the Sturmey Archer hub with an Sram or Nexus, since they can be shifted while pedaling, wheras with the S/A, you have to stop pedalling to shift, which is very annoying.
I bought the Downtube because I love the way it looks, and I love 16" wheeled bikes. I still like it, but I'm very disappointed with the quality. That's something you just cant get a feel for by looking at pictures on the internet. I realize that the Downtube was 1/2 the price of the Dahon, but I'd have gladly paid more for a better quality bike. I'm not trashing Downtube, but you get what you pay for.
So by all means, try to look at one in the flesh before buying. I remember the signature line from a fellow motorcycle rider on a BMW forum: "Buy the best, cry once." Sometimes buying the less expensive item can cost you a lot more in the long run, both in money and grief.