I have the Cobalt 2 post in a 400mm, no setback version. The post is bored oblong, with thicker front and rear walls, making it very stiff for its weight. It is so stiff that I can run it fully extended on my dirt jump bike if I use it for a trail ride.
One area of special concern is the unique clamping mechanism. While I generally prefer a micro adjust clamp (ex. Thomson), I found the system on this post acceptable. It was somewhat difficult to adjust given that it rotates around a fairly long radius with no tensioning system to assist adjustment. Additionally, the clamp uses a T25 Torx bolt to hold the saddle rails, which can be inconvenient if the saddle angle needs readjustment.
That said, the stiffness and lightness of this seatpost satisfy my basic needs.