Intercoolers / piping = good.
Manifold = poor fit, require modifications to make work, but in the end acceptable
Turbo = typically cheap / poor, but many last well beyond expectations
Wastegate / BOV / boost controllers = bad, typically poor copies of older designs
The largest problem with ebay kits is their lack of solution for fuel / spark control and other supporting mods. Even top notch quality components will fail almost right away without:
- wideband O2 sensor & controller
- much larger injectors
- new ecu control of fuel / spark (typically stand alone engine management or custom chip)
- full exhaust solution (downpipe, larger pipes, new cat, high flow muffler, $$)
- oil supply and drain solution for turbo (and water supply too if water cooled turbo)
These things are the most challenging to a turbo build, which the ebay kit completely fails to address.