In researching the specifications of both the Dahon folding cycle and the Brompton it is possible to identify some areas of their design that would indicate that they are offering a slightly different solution to a problem and as such will attract an end user with perhaps different priorities.
The Brompton's design seems to focus on having a unit that when folded is as compact as possible and can easily be transported with the drivetrain stored in a position that keeps the oil/grease away from the user. The way the rear struts are hinged at the bottom bracket allowing the rear wheel to swing underneath the frame is very effective, and as well as aiding in the ease of folding the bike it also offers a practical use as a stand. The use of 16 inch wheels throughout the range of cycles indicates that compactness is of the utmost importance. This might seem obvious in a folding bike design, however any cyclist knows that a larger wheel offers a more refined ride and is more stable. Another point is that the Brompton has more hinged points than the Dahon; this allows for a more compact cycle when folded but obviously takes slightly longer to fold and unfold. The other thing I noticed about the Brompton was that it still utilises a winged bolt arrangement at the hinges which might be lighter and possibly more compact than a quick release alternative but will take longer to undo and secure.
In comparison the Dahon comes with larger 20 inch wheels as standard, offering a better ride but obviously are always going to be physically larger to carry. It has less hinges and are quick release in function so offer a slightly quicker and less tricky transformation procedure, but its arrangement won’t allow as compact a form as the Brompton's.
Another point worth noting is that as more hinges are introduced into the design, you could be compromising the strength of the structure