That's a tad unfair really, since out of the box it does work. The only real problem I encountered with the two HK416s that I received was the magazine itself is slightly to far forward, so it has trouble aligning to the hop-up unit. When I used a regular airsoft M4 mag, it worked fine. Also, a problem with most china made guns, is that it's firing hot, both of them were firing consistently around 380FPS.
Another than these minor problems, out of the box and with the 9.6V battery that it came with. It performs ok, a nice trigger response on semi, ROF isn't great but not too slow. A tough