I work at a collision shop and have had many dealings with them, mainly headlights, once in a while on fan assemblies. As far as lighting goes, they are Ok at best. In the box they will look fine, trying to fit lamps on various vehicles can range from good to very poor depending on car. In the yukon/tahoe case, I would say they will be ok, although a proper headlight aiming with a machine will provide mixed results, meaning sometimes they will point straight after aiming and sometimes they will be out of alignment with the grill noticeably. Also, I dont think the UV clear is as good a quality as the OEMs, and they have the potential to fog over more quickly. If this does not bother you, then go for it.
As for the fan assemblies, it is the opposite. Appearance wise, the plastic looks cheaper and thinner, and isnt always braced the same as OEM. However, in the 18 years I have been working here we have never had one come back for a bad fan assembly, so I would say mechanically they are as good as anything. And I have never had one that wouldnt bolt up either, so I wouldnt expect any fit issues here either.
Hope this helps.