I just had my Tamron 500mm out last weekend. I finally got around to getting a manual focussing screen for my 6D, and wanted to try it out with the mirror. I found that I could get acceptable focus more often than not (the opposite of my results with the normal focussing screen), and I guess the f8 aperture helps with that by giving greater depth of field.
Once I had my confidence up, I tried to capture some shots of the dog - I had no success in getting accurate focus on the moving dog.
I originally bought the lens to shoot a solar eclipse. I didn't have the money for a decent refractive lens at the time. The image quality is pretty good - sharpness is acceptable, contrast a little low (but easily fixed in post), and avoid out of focus specular highlights, unless you like the doughnut effect.
The main problems were always focussing, and lack of light shooting handhed at f8 and 1/500. Both easily fixed by shooting on a tripod and using liveview (but not as fun).