If you don't know if you need a folding bike, you probably don't need a folding bike. It's kind of compromised as a bike, and if the (admittedly huge) utility of it folding isn't painfully necessary, it'd be hard to justify owning one.

Once you get to the point where a folder is unavoidable, you may as well get a good one, be it Bromptom, Dahon, or whoever. At that point it's definitely a buy-once-cry-once kind of purchase. As much as I love mine, I wouldn't recommend anyone buying one who isn't already really into cycling for transportation rather than sport and doesn't really need a folding bike.

And yeah, the low end of the market is pretty crap, much as it is for regular bikes.