I bought it as a compact and lightweight replacement for the Sigma 150-600 C on mountain trekking tours, where every gram counts. In fact, it is a reduced copy of it and is a compromise between range on the one hand, and compactness and weight on the other hand. The picture quality is the same. Does not require getting used to when changing optics. Due to its compactness and weight distribution, the photographer, when shooting handheld, can stabilize better than with 150-600. Is a more versatile tool for filming: -You can shoot on the go car. With a size of 150-600, this will not work. -Insects can be removed without departing from them, when I saw, as from 150-600. -400mm is plenty for shooting birds and wildlife. For me, a wardrobe trunk and a tripod foot are extra money in the cost of a lens. I have my own proven cases and I only take them off my hands.