The Sirui K-40X exceeded my expectations for smoothness and ease of use. It is well made, finished and works very well. This was purchased specifically for use with a large DSLR and Tam. 150-600. The large ball head locking knob offers excellent control over friction and camera movement. A small screw on the side of the handle allows you to set the minimum friction to a predetermined level. This works great as you can go from full lock to a smooth motion without losing your camera in free fall. It takes about 1/4 turn of the knob, fast and very controllable as it should be. Panning is difficult, but with the weight of the large camera and lens, it moves fairly freely. I don't want him to pan more freely than he does. Pan-lock thumbscrew basically works or not, it doesn't work well to adjust friction gradually. Initial tests with the Sirui K-40X ball head showed that mass and stability greatly improved the apparent sharpness of my photos when using a 600mm telephoto lens (greater "storage rate"). I think this is probably overkill for many users with light cameras and short lenses, and as some have pointed out, hard panning without a big camera and lens can definitely be an issue. You can find a good comparative overview of ball heads under DPR, ball head search.
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