here it is simple, you want good parts for certain things. Ebay headlights work just as good as oem (mostly) but ebay wastegates are not in the same quality control standards that more expensive brands go for. they look great function most of the time, but have a much higher fail rate, and do not last quite as long as lets say a Tial wastegate. I have all brand name parts that are essential to the operation of such a costly investment. the wastegate is THE MOST important part of the turbo system. A failure there normally resuslts in catastrophic failure. Now im not saying that you cant have other parts fail and produce a failure but the operation of the wastegate is critical in a turbo application. Therefore i only choose quality when it comes to things like that.
Remember the old saying "Fast, Cheap, Reliable" you can only pick 2.