IMO, you need support for both stability and easy of use. I've not held that Tamron, but looking at photos and the weight of the lens, a good ballhead will easily provide enough stability. As far as ease of use (panning, movement, relieving weight), a gimbal will really help, but for the size of that Tamron, I think it's overkill.
I purchased the Wimberley II for my 200-400 which is a bigger lens than the Tamron. Even with the 200-400, I could have gotten away with a ballhead. The main advantage with the gimbal for me, was easy of movement and peace of mind (you don't have to worry about locking the ballhead really tight to prevent flop).
This is less of an issue and some will laugh at me for saying this, but that Tamron will look a little odd sitting on a big gimbal.