We see a lot of these (mostly Chinese) bikes at the university. Overall, they are ungodly heavy, being made of the fines "hi-ten" steel or very thick-wall and low-grade aluminum.
The components are the cheapest available, there is little or no alloy on the bike (often even the hubs are pressed steel), and the brakes are, as noted, dreadful.

All that being said, if adjusted properly and lubed frequently, they will give good service for a casual knock-around. Kids here use 'em to get from the dorms to campus...they're fine for that.
From my standpoint as a mechanic, they are hardly worth working on. By the time you figure parts and labor for anything more complex than replacing brake pads or fixing flats....You might as well just buy another one.

Getting one from the store properly set up is a minor miracle; usually they hire young lads with minimal skills to throw these things together.