The Trinxx weighs in at 32 lbs., that is pretty darn heavy for folder, but that is probably reflected in the price as well. The second one claims to be "lightweight", but i don't see a weight listed. The Dahon is very nice, but doesn't seem to belong in the same category with the two inexpensive bikes.
There are a lot of options out there that are not as pricey as the Dahon, but still lightweight and high quality. Take a look at www.origamibicycles.com