Hope I've said enough about the good side. At 80mm, it is soft when wide open. The sharpness improves as being stopped down, but no significant improvement for corner sharpness throughout apertures. Center sharpness improves when zoom out. At 200mm, center is slightly shaper then corners at wide aperture and even out when stopped down.
Worst situation is the short end at wide open.
The lens has slight light fall-off at wide apertures. But, in most cases, the light fall-off is not obvious. The worst is at the 200mm end. Also note, it happens that this trim has dark coloring at the edges in the picture, so look at the lower corners for a more precise sense of the light fall-off. For 2x TC, I've only bad news.