The Sigma 150-600/5-6.3 DG OS HSM S feels like, and is, a solidly constructed lens. It's fully weather sealed with sealing on all the control switches, rotatiing controls and front and rear elements. The controls are smooth operating and precise. For example, the manual focusing ring has a very smooth and frictionless action with no backlash. The control of focal length can be accomplished either by rotating the zoom ring or the lens can be zoomed using a "push-pull" action. The "push-pull" pull action is again very smooth. One downside of this is that it does mean that there is some zoom creep when the lens is pointed up or down my more than about 45 degrees. However, Sigma have provided zoom lock ability at any of the marked focal lengths: 150, 180, 200, 250, 300, 400, 500 and 600mm. The lock at 150mm is a solid lock and at this setting the lock must be deactivated in order to zoom the lens, This is to prevent any zoom motion when the lens is being transported. At the other focal lengths the lock "soft" and the lens can be zoomed by a firm rotation of the zoom ring. It's more of a "click stop" than a solid lock. This allows the zoom to be locked, but quickly zoomed to another setting without having to first disable the lock.
The rotating tripod collar provides excellent support for the lens. Rotation action is smooth and there are click stops as 90 degree rotation intervals which can aid rapid switching from horizontal to vertical orientation. The tripod collar is not removable, but the tripod foot can be removed if desired. A larger feet with a built-in Arca-Swiss compatible quick release plate is available.
The lens hood is a solid metal cylinder rather than the thin plastic hood of the Contemporary lens. It attached to the lens with a thumb screw, in the same manner as lens hoods for the Canon prime telephoto lenses do. Also like the Canon telephoto primes, the lens hood is a sleeve which slides over the lens good rather than a cap which clicks into the filter threads of the lens.This allows the hood to be attached and removed while the lens hood is in place.
Both the Sports and Contemporary versions of the Sigma 150-600/5-6.3 DG OS HSM share the same set of control switches.
There are three focusing modes - Manual, AF (with full time manual focus option available) and an unusual third mode - "manual override" - in which manual focus takes precedence over AF at all times, even during the AF process and during high speed continuous shooting.
The Sigma 150-600/5-6.3 DG OS HSM S (Sports)) has three focus ranges. For general work there is a 2.6m to Infinity (the full AF range) setting. However, if you know approximately where your subject is likely to be you can speed up AF search by restrichting the range to 2.6m to 10m for subjects that will be close, or 10M to Infinity for subjects you know will be more than 10m away.
The lens has three stabilization (OS) modes - Off, Normal (stabilized on two axes) and Panning (stabilizes on one axis). Accelerometers tell the lens which axis to stabilize when in the panning mode depending on the orientation of the camera. Panning stabilization is effective only for horizontal panning, but the camera can be in either "portrait" or "landscape" orientation. The viewfinder image is quite "fluid" even when stabilization is active, but the system words well, giving ~2 stops of stabilization at 600mm and at least 3 stops at 150mm for me. Depending on how steady your hands are you may get slightly different numbers.
The final set of control options, marked "Custom" in the image above, have "off", "C1" and "C2" settings. These are used in conjunction with Sigma's USB dock. Using the dock and software running on a PC or MAC, a user can update the lens firmware, modify the lens focus speed, stabilization characteristics and can set a user defined focus range. These users defined settings are stored in the lens and accessed by the C1 and C2 custom functions. Additionally the USB Dock system can correct the lens for front or back focus if you find any (I didn't see any in my testing).