I'd say they are a good bang for the buck and that you would pay quite a bit more to get better ones. It makes me wonder about their mics.
I've owned some Superlux 668B headphones for about 3 years. Yes, they're pretty decent value for money, but they aren't very sturdy. The predetermined breaking point is the upper part of the cable which is made out of soft rubber. Sooner or later it's bound to break and the upper part of the cable can't be replaced.
I'm glad I bought some ATH-M50x headphones after the Superlux 668B died. (Considering their build quality, their form factor and last but not least their superior sound). They're 3-4 times the price of the Superlux, though.