I owned the Tamron 150-600mm and used it with my 7D and 5DMK3. I also still own the 100-400mm, and have used it for tens of thousands of shots over the past five years.
I returned the Tamron after a couple of weeks and a thousand shots because it did not track BIFs or simple action with the 7D with any kind of reliability. This is a known issue. I found that it didn't work very well, especially compared with the 100-400L, on action shots with the 5DMK3 as well.
That said, on static subjects, the lens was quite good with both cameras, and a real bargain if that is all you have requirements for.
I really wanted to like the lens as I thought the build quality was very good as well, the weight was manageable, and the general interface was very acceptable.
I am hoping that Tamron fixes this issue, and have a preorder sitting with a vendor with the expectation that the seemingly long delay in getting these lenses out to dealers is somehow related to a fix being implemented.
So I will be doing what I did and I recommend you do the same. You will know pretty quick if the lens is misbehaving with your 7D. I don't like messing with TCs on zooms much, especially relatively slow ones like the 100-400L.
There really aren't many viable higher quality low-budget options beyond 400mm, so I can see where the Tamron hits the sweet spot. I rented a 400mm DO which alone produced images superior to the 100-400mm, but not enough to make me flip for a purchase. I also tested it with the latest 1.4x Canon Extender vIII and was disappointed with the lagging performance for BIFs.