I have both bought and been given some of these "knockoff" sets, and while the resulting build. The resulting build is pretty, but fragile. The tolerances on the bricks are bad, to the point that some required a lot of force to join, and others are so loose that they can barely carry the weight of the bricks on top. I have also consistently found at least 1 brick that wasn't molded fully, and was therefore useless, with no spares. The colors are also usually quite uneven. The instructions are usually fairly easy to follow. But the build methods are bad. I often see bricks stacked directly on top of other bricks, with no interlocking, resulting in whole walls being able to easily fall over.

The knockoff are fine if you don't have the money to spend on Lego, but you really also get what you pay for.