I received my first PCBway order yesterday. It looks reasonable so far.
It is a relatively simple design: 4 layer FR4, 8/8, 1oz, 10mil holes, green mask, irregular routing. The holes are precise and the registration of copper to hole and copper to mask are reasonable. The silk is legible but not amazing. In general, I don't really care about the silk being an art project as long as it is legible.
The order was an experiment to see how they do. So far (before assembly) it looks good. The schedule was met - shipped in about 5 days, arrived 3 days later. The cost was ~60% less than a USA based option. After I assemble and test, I will know for sure - but the outer layers look good with 8/8 trace space. Assuming all goes well electrically, I will decide if it seems safe enough to send my more critical designs with tougher features and expensive IP. I am not terribly surprised that they can make PCB's, but I am definitely worried about my designs making the rounds. It would not be too challenging for anyone to figure out what this is used for, copy my firmware and slash the cost.
I am far too small to implement a security scheme to outwit copycats.