Let me add that the warning you quoted, "It will only work on disks that are exactly the same in disk geometry, meaning they have to the same model from the same brand." only applies to moving an image between disks and keeping it useable (look at the context it is used it). It should be obvious that the seccond command in the example would never work if the source was a device (entire drive) and the destination was a file on a partition on the same size drive. I your case the drive geometry becomes the same when you put the image back on the same physical drive that it came from, the image on the larger drive is only temporary storage.