I have both the 8X and 10X Ziess SF and think they are a solid product.
Some of the concern may be due to the fact that Zeiss uses a composite material for the eye cups rather than metal and so the thought of plastic comes to mind. I like the composite approach better because if it is dropped on the eye cup, the eye cup is more likely to break without damaging the eye piece threads compared to using metal. Then it is just a matter of removing the old eye cup, calling Zeiss for a replacement, and then screwing in the replacement a few days later. Damaged eye piece threads means sending it in for repair. Lee put together a nice write on replacing eye cups that also applies to the Conquest.
I've have no concerns about the build quality. Any issues would most likely show up at the time of purchase. All manufacturers can have failures but I do not see the SF as being any more trouble prone as the others. If an issue does come up, Zeiss is good on getting it fixed.