When others post similar threads I have found the responses informative so here is mine. First, I travel a fair amount so I would buy the lens with miles through the airline catalog. While not free and a fairly poor value for the miles, it will not be a cash purchase. I have a lot of miles. Second, I shoot everything from landscapes to sports inside and out to portraits, wildlife and everything in between. And, somethings on the same outing. Third, I have a full frame and APS-C. Fourth, I already have the 70-200 2.8 L, 300 f 4 L , 24-105 f 4 L and the 1.4 and 2.0 teleconverters. I like the 1.4 teleconverter but the performance of the 2x is not as good for, I think, obvious reasons. My thinking is that I can get what is apparently a very sharp and versatile zoom for low cost and by doing so cover, on the full frame alone, cover a wide range of shots with just the 24-105 and the 100-400. In fact, if I had it last week while in South Africa, those thee items are all I would have taken. What do you all think?