Well I've installed a third party crank angle sensor and an ABS sensor on my Corrado recently and both are fine?
No idea what that says.

That says you've bought some cheap sh!t and it worked.
I've bought some cheap ABS sensors for a Clio I ran about it, been spot on. Also bought 3 super cheap coils from ECP. One after the other and one packed in after two months, replaced with Valeo then replaced the 4th one with Valeo and been golden.
It's all hit and miss with cheap parts.
I flat out refuse to fit cheap thermostats from ECP, GSF or anywhere these days, ALWAYS seem to have issues.