I bought these as well as the t.bone HD 815 headphones which are in a very similar price bracket. I also own a pair of Beyerdynamic DT770 Pros that are about three times the price! These are clearly trying to copy the Beyerdynamics in design.
Sound quality: They're pretty decent, especially for tracking. They don't have much sub-bass reproduction, so they miss a bit of punch compared to both the other two. They are quite bright though, with lots of clarity in the high end. Sometimes it's a bit much, with the sound coming across a little bit brittle and harsh in some situations. The soundstage is wider than the t.bones, but nowhere near as expansive and detailed as the beyerdynamics. They work well for classical especially, but they're pretty decent for everything unless you want loads of punch out of your basslines. The sound isolation is as good as the beyerdynamics.
Build: Mostly great for the price. All the materials feel good quality and robust. I think the cable feels a little flimsy, I suspect the actual conductors inside the cable are very thin, which might lead to durability issues if these get shoved inside a bag regularly. There's a couple of hard edges on the pieces that connect the headband to the speakers, but the biggest complaint is the shiny plastic on the lower half of each speaker enclosure: it feels fine, but looks cheap and is an absolute fingerprint magnet. It's a really annoying feature of an otherwise well designed pair of headphones.
Comfort: Nearly as good as the beyerdynamics, which are the most comfortable pair of headphones I have ever worn. Absolutely no complaints here, you could wear these for a long time and not have any complaints.
Overall: A decent pair of headphones, which if you prefer an analytical sound that borders on harsh over a somewhat muddy sound would be a good choice over the t.bones.