I needed to get several pairs for a recording session, so I got some of these and some of the Superlux HD660 Pro at the same time. I've also got a pair of the much more expensive Beyerdynamic DT770 Pros to compare to.
Sound Quality: They sound good! They feel fairly flat in the highs and upper mids. They have a bit of a bump around the lower mids, which can make funk sound a bit muddy, and might get fatiguing if you're listening for hours on end. Their soundstage is quite enclosed, with the sound feeling like it's coming from inside your head rather than around you. Compared to the Beyerdynamics they do feel muddier and less precise, but they're pretty respectable, especially for electronic pop music, where the bump in the lower mids serves to accentuate the synth bass lines. The sound isolation is not quite as good as the superlux or the beyerdynamics but is definitely nothing to complain about.
Build: No concerns at all. The braided removable cable feels nice and strong (although came folded rather than coiled which is a shame). The headphones themselves have a decent weight to them, with plenty metal in the headband and the plastic doesn't feel as cheap as I was expecting, though it doesn't feel as premium as the beyerdynamics. They feel maybe slightly better quality than the superlux ones, but look slightly cheaper in design. All the stitching in the faux leather looks to be good quality.
Comfort: Really good, to my surprise. They fit on the head very comfortably and don't pull awkwardly or put pressure in strange places, and the headband has a lot of adjustability so I'd expect these to be comfortable on most heads. The earcups are deep, which means that if your ears fit inside them (and most should), they don't get pushed against the side of your head. The warmth of the leather earcups means that they're not quite as comfortable for long periods as the superlux, but I could still wear these for a few hours and not have any complaints.
Overall: A really solid pair of studio headphones for anyone on a budget. Buy these over the superlux if you prioritise a punchy sound over precision and brightness