Here's my two penneth...
I've owned two Dahons and had no end of problems with them. Both were 26" wheeled Matrix models with alu frames.
The first was a 2009 'lockjaw' model. From memory, this was certainly up there with the cheapest of the Bromptons price wise at about £800 (on the ride to work scheme). However, I had to spend a fair bit on it to keep it going - including having the wheels trued on an almost monthly basis. After having the front and rear done about 6 or 7 times each (at £10 a time), I eventually upgraded the wheels to some Mavic CrossMax and they ran true throughout the ownership of the bike - about 4 years. But that added to the ownerships cost of the bike by a total of about £300 - so we're now at £1100.
Then the frame developed a small crack just about the time that Dahon were getting into trouble.
Evans were useless at helping me out as they no longer stocked them and at that time, no one was importing them. I had a 5-year frame warranty that wasn't worth the paper it was written on. My only option at that time was to pay for the bike to be transported back to Dahon factory in China and hope that there'd still be a company to honour the claim. On the information I was given, it estimated that it would take them around 3 months to even look at the bike and there were no guarantees they'd ever do anything about it. There was talk of another importer possibly offering the warranty I needed. The advice I was given was to wait out that deal and hope for the best.
However, as cycling saves me around £250 a month in parking and tube fares, I didn't want to be without a bike for any length of time as it would end up being cheaper to just buy a new one.
So I ended up buying another Dahon Matrix from a work colleague. this time a 2008 model Matrix. Knowing the history of the bike i knew that it had been ridden less than 50 miles in the intervening years.
I rode that for a year and then the frame actually snapped on that.
That was so bad that I junked it. And then went back to my original Dahon as it was cracked rather than snapped and rode it for about a year until that too completely failed.
In the end, I threw away both bikes, salvaging my upgraded wheels and little else.
It was then that I decided to take another look at Bromptons. And ended up buying an H6L for £1080 on the ride to work scheme. So far, I've had one wheel wear through and split - which I didn't expect, (but seems to be down to cycling through horrible London sludge and not cleaning it often enough, but otherwise it's just been consumables - new chain, sprockets and chain ring at £50.
It's just as fast, is just as comfortable, and folds up far smaller which makes more sense for me.
So, for me, I wouldn't recommend a Dahon to anyone I'm afraid.