I don't this is the same leveling base, MR was talking about, though, he must have covered most good equipment here.
I bought the 1321 leveling base, based on his review, but the one pictured above is from one of the newer Gitzo's which has a sort of buildin leveling base, not sure if it gives your the same flexibility, but definately it is a lighter version.
Well, I bought mine, and its always attached to my 1548 legs, but I must admit, I don't use it as much as I had thought. It was originally to help me leveling my camera up when trying to make images for stitching.
Henrik