This is a great lens. It is super-sharp at every setting and covers such a huge range and focuses so fast and so close that it can replace several lenses — if you don't mind the huge size, weight and price.
You don't need a tripod unless you're using teleconverters. I easily hand-hold this beast with its excellent stabilizer at 600mm.
At 60mm, not super sharp, gets purple fringing. At 600mm,it is super sharp, no edge fringing. Beginning around 100mm, it's good. Overall very good lens and happy with it. But it's $2000 at 6 pounds and not so easy to use due to weight. If you think of it like a 100-600 vs a 150-600, he like's having that extra 50mm range.
Personally, I don't see why I'd lug 6lb around vs 4lb on the 150-600. At 6lb, I'd frankly step up to a 500mm f/4 (like the Sigma at 7.6 lb or a used nikon G at 8.6 lb). I don't think I'd like carrying 6lb plus camera and gear for a long time.
I'd rather carry a separate RX100 (under 1lb with lens and battery!) or similar for the 24-200 range and keep a 500mm f/5.6 or 150-600 on the DSLR. Usually, for me, the shorter focal lengths are for people I'm with and the longer are for wildlife, and I can keep the camera's setup for those different purposes.
I am with Marc on this: I am used to carrying a 200-800 equivalent lens on the camera with a 24 to 120 equivalent second lens. Putting it all together into one lens with necessary compromises and extra weight does not appeal to me. The phone covers the low end when I do not want to change lenses on the camera.
It looks to be as sharp as any of the other prosumer superzoom telephotos. I would find this focal range quite handy (if only someone made the mythical 10-60mm f2.8 wideangle zoom to compliment it! , however I'm certain it's not worth carrying the extra 690grams (one third!) weight around.
Kudos to Sigma for trying to keep the weight down by using TSC (thermally stable composite) etc in its construction - but it's just too heavy for me. For only another ~300grams I'd be more inclined to cart a 600 f4 around (once Nikon finally catches up to Canon and Sony, or I jump ship).
I'm hoping that Nikon will soon come out with its PF 600mm f5.6 at around 1.75kg. Nearly a kilo lighter than this Sigma will be compelling. I will miss the zoom capabilities but not the weight, (even a reduction in weight and length of the Tammy will be welcome).