Turbos spin up 100,000rpm, red hot and require a 100% perfect balance, its not uncommon that after testing one it fails, there are so many variables that have to be exact, and running it is the only way that they know its right, the materials they are made of, the machinest, the right install, are all varible as well. Everyone wants 100% quality, industry is happy with 98%.
A well known company, good at its work installs a turbo, the turbo fails, they ring Garret for warranty, no luck, they wear it.
Slides a better deal by far than them.