I think - aside from production issues that I've seen first hand (holes drilled off, threads screwed up, etc) - they work for some whose combinations are milder or who don't push their equipment very hard. I agree - cheap junk. But for some, stock parts would work fine and yet they "upgrade". So somethimes cheap junk will work just fine. Just inspect very carefully.
I agree with Moper. Some just don't push their stuff hard enough to find the weak links. For every one guy that says that kind of cheap Chinese stuff works great, there are half a dozen guys that can give you a horror story.
I have 440 Source rockers on my daughters bracket Cuda. One of the adjusters recently broke off with the locknut, and luckily came to rest beside the valve out of the way of the spring. I now carry a spares but plan to upgrade to Harlan's when the Indys get ported. They are rather noisy.