I owned this lens for about two weeks in March. During this time I tested it for both static subjects and moving subjects in excellent light with my 7D and 5DMK3 bodies. I have several years experience shooting sports and birds with the Canon 100-400mm L and the Sigma Bigma (50-500mm) lenses.
The Tamron was a very mixed bag. I enjoyed the feel-in-hand, the weight was reasonable considering the focal range, the quality of materials was very good, and the price was a bargain--if--you are OK with it not functioning very well on BIFs. After at least 1000 shots I found that it would not lock on a moving bird in the 400-600mm range with either camera. Whereas a few minutes prior it would provide very acceptable results on an easy-to-focus static Great Blue Heron or a sparrow. I grew too frustrated and returned the lens during the allowable window.
That I have seen some great BIF results from others, makes me wonder if the quality variation is vast among copies. I've also considered purchasing another copy, because this lens' focal range at this price point is valuable.