Since buying this head, I've quickly learned to love it, especially after buying the necessary hardware that allows me to invert it as needed. The smooth design, reliability and light weight has helped it find a permanent home atop my Gitzo GT1542 Mountaineer tripod, supplanting the GH1382QD ball head that came with it.
Some first impressions after picking up an Arca-Swiss P0 Ball Head recently. Why? It's interesting. It's an inverted design so that the panoramic base is above the ball, ensuring a level platform for panoramic photography. Basically it eliminates the need for a leveling base. Combined with the 9oz weight, it'll reduce as much as 1.5lbs from my systematic tripod setup. I quickly discovered the reason for the weight savings: the base of the ball head is made of polycarbonate, most likely Delrin. The rest is made from either magnesium or aluminum, depending on the part. Regarding the design, it also has no protruding parts beyond the pano lock lever. The ball lock is performed by a rotating collar around the middle of the body, resulting in a sleek design. The ball is also aspherical, a feature used across Arca-Swiss' whole line, that increases friction to prevent your camera from loosely flopping over when the ball lock is loosened. A very elegant solution to a universal issue with all ball heads.