I won one in a competition a few years ago I have one of the kirk king cobras as well. I have been using the Calumet one with my canon 600mm f4 I.s. for probably about 4 years. It's done the Cairngormes numerous times, Poland,Sweden, Cuba to name but a few of the places it's been used and abused. I can only say as I find it's done everything I have asked of it.