I have 3 Dahons. All reliable. They all ride like proper bikes, not some circus toy.

I suspect the real reason that you come across so much criticism of Dahons is simply because they sell more folders than anyone else.

They like to innovate, and occasionally make a turkey, but my impression is that the majority of complaints come from people who haven't bought through a bike shop, so they are buying a bike that is not properly setup in the first place.

One problem with folders is that they do have special requirements for maintenance. There has to be compromises to make a bike fold. They require intelligent maintenance and if they don't get it, they become problems.