After watching a few videos on this lens, I am seeing this as an alternative to the 200-600 and 400-800. It is a similar size to those lenses, and with TC's can produce similar focal ranges and seems to be sharp with the TC's. In some ways it provides advantages to the 200-600 and 400-800. It seems to be as sharp or sharper with a 1.4X compared to the 200-600mm per Dustin Abbott. It then has a broader focal range than the 400-800mm with the 2x. Interesting, but does not seem to be a replacement for the old 100-400mm given the size.