The Nexus 7 hub is likely to outlast the Dahon. The Dahon designs seem to eork well until they wear out. At that point they are frequently scrap as the part that has worn wont be replaceable. Whilst cheaper than a Brompton, the Brompton wearing parts are sacrificial and replaceable. If it has low miles and it's cheap then it will be a sensible buy, i echo the need to take the pedal pressure off when changing gear, but when something that isn't a normal bike bit breaks, it's pretty much scrap unless you are happy getting creative with frame parts
Now, as the owner of my third Dahon, I know exactly what you mean, but would qualify that remark. Dahon has, to put it mildly, a poor record of support for older models, particularly with frequent model changes, multiple changes of distributor. There have been more than a few issues with quality of the model-specific parts, that are of course the ones that are harder and/or more expensive to get hold of. My Jetstream XP- frame latch broke (replacement sourced by LBS from then distributor Fisher), and the (model-specific, but Cane Creek manufactured) rear shock stopped holding pressure. Cadenza- frame latch broke (replacement from Fisher, again). Chutney my Speed Pro TT- Henrik the first owner needed the frame replacing under warranty, then it needed a new crankset when I bought it as the left arm had got damaged (FSA set as per original fit bought without problems), and since I've had it the chain guide broke and I eventually got one from a German dealer because no UK dealers seemed to have them listed. Front (calliper) brake seized up and needed replacing a couple of times, but that's nothing Dahon-specific, I eventually got a new fork with V-brake mounts, which were a better option, when running 40mm tyres as I do, anyway.
The qualification: You can get hold of many parts for older models, though you might have to be look further afield- imports etc (eg
this lot).
CH White have the best selection I've seen in the UK, I've bought a few times from them over the years. A lot of Tern parts are interchangeable as well, which helps. Chutney now has a Tern fork (I had ummed and aahed about getting the Dahon one then they disappeared from sale), and it was a perfect fit. There are plenty of 80s and 90s Dahons in regular use to this day, let alone newer ones....