[westopher]

There is heat transfer issues as well, but yeah, it leaks or it doesn't, and shittymoto products leak. They also fit poorly and the welds look like they were done by a blind, one handed sloth.
The plastic/aluminum, OE/aftermarket comparable are:
Thermostat housings
Expansion tank
Radiatior necks

Aluminum thermostat housings have casting issues and are usually warped right out of the box.
Shittymoto expansion tanks just don't fit
The plastic rad necks are resilient until you have motor mounts that are beat to shit. If the motor shifts way too much on acceleration it will crack the rad neck.