Rand, loaned me one of his for some testing.
Here is what it looks like on a 600EX-RT on top of a 5DIII with ambient at least 2 stops below.
We were getting ready to do table shots. The model is one of my fellow photographers on this job.
As can be seen by the shape of the shadow under her chin, the biggest benefit is getting the light source well above the lens axis.
The fact that they have a block right at the point were the flash head ends inside is a plus for even light. Not my first choice for a modifier but it worked well for the table shots.
It also worked well for small product photography, which was one of my primary interests, and I think that's why Rand got them to begin with.
please log in to view hosted photos in full size.