Well right now it is priced at $1,069.00. And all we have is a few prototype reviews to depend on. I will wait 6 months for actual reviews from photographers and may be slight price drop. It is not going to stay at that price forever. At the end of the day it is tamron and price will drop a lot sooner than any counter parts from canon. But even at $ $1,069.00 its not a bad deal at all.
Another lens to compare this tamron with would be the Sigma 150-500mm F/5-6.3 APO DG OS HSM. Its also priced at $1069 at amazon however I don't see very good reviews there.
I had the Sigma 150-500mm, and up to about 400 mm it was not bad at all. However given the weight and overall performance I'm a lot more pleased with the 100-400 that I bought to replace the Sigma.
5D3, 5D2, G5X, G16 | SY14/2.8, V20/3.5, 28/2.8 IS, Ʃ35/1.4, 50/1.8, 50/1.8 STM, Ʃ50/1.4 EX, 100/2.8L IS Macro, 16-35/4L IS, 24-105/4L IS, 70-200/2.8L IS II, 1.4x II, 2.0x III, T28-300 VC PZD, 70-300L IS, Ʃ150-600 OS HSM S