For me, the only con on a long lens is usually the weight, but this lens is surprisingly agile and I can even hand hold it for the most part, although I did add the tripod collar for those times a tripod or monopod is needed.
I had previously rented this lens and compared it with another popular one in the same focal length. This one has a small advantage on the largest f stop, plus I checked various reviews and settled on this one being the one I wanted, and could afford.
Very happy with my Tamron 100-400!
Never thought I would be buying a third party lens, but after reviews and much research I pulled the trigger and to my surprise it is sharp, well built and cost effective. Also weather sealed. A good option than spending twice the money on the cannon alternative. Lighter too buy a pound. The is works great. Getting shots at lower shutter speeds is a plus. I don't think you will be disappointed!