I've used one for those moments when a subject is harshly backlit, yet insists on having a shot taken anyway.
The example I have in mind is outdoors in broad daylight, with the subject standing in full shade. Either the background will be tremendously blown out by exposing for the face, or the face will be unacceptably dark if exposing for the background. Such a condition is manageable, but when the subject demands the shot anyway, the flashbender can help with fill flash. Instead a "direct fill flash look" to the image, the flashbender serves as a nice bounce surface, softening--so to speak--the light on the subject. Though the direction of the light is undeniably from straight on, the result is less undesirable than using flash aimed directly at the subject.
The large flashbender can be used as a snoot, and that capacity may add to the usefulness of the Rogue product for you. I have not used the diffuser.