Having had this Tamron for a month now and reading about it in plenty of forums, it is nice to read a review that independently corroborates what testing has shown in skilled hands so far. Winter weather has made it difficult for people to get out with the lens and do much shooting and comparisons with other lenses/bodies.
I found I also like the lens best when not shooting all the way at 600mm. MFA on my 5Diii was a startling -17 on both wide and tele ends. Way out of the norm for the small handful of lenses I own so far. BUT, as long as it works, I'm certainly OK with it. The 6 year warranty does provide a certain amount of peace.
Coming at the time when I was wanting to buy my first long lens, it was great timing, the Canon 400mm f/5.6 had been squarely in my sights over the 100-400mm zoom. Image quality was more important to me, figuring wildlife would be farther away as a rule and I would be resorting to cropping fairly often anyway. I would enjoy the lighter 400mm, but this Tamron gives me some flexibility for closer shots while retaining good images in the center at a distance. A new Canon 400mm would run around 30% more, and I would also need to buy a 1.4x extender in addition.
The Tamron has helped me save money and provide comparable quality in the price range I was looking at. All pluses for me at this stage in my shooting (and income level).