I wouldn’t worry much about the brand of the derailleur, both the Dahon and the Altus derailleurs are perfectly adequate, unless you are someone who comes from a background of motorcycle riding, and shift your bicycle as often as you shift on a motorcycle. If you ride a lot of bikes, and use the gearing all the time, you would notice the difference in shifting performance between different levels of components, and likely choose a bike with higher-end components, or swap them onto your existing bike (drivetrain upgrades are not hard to do).