Following on from my comments on the DiffCase, Jim Armstrong from DiffCase got in touch to let me know that they have produced the following video to address mine and others concerns.
Having used the DiffCase in anger, I can say that it performed extremely well. My wife managed to drop my iPhone from about 3ft and the phone and case stayed intact, and this past week I used it for a video shoot, and the light shade was perfect for the job. Whilst the DiffCase does still have some design issues (access to the connector is a real problem), I have found it to be a very useful case for shooting video and for providing good all-round protection, but it's still not quite an everyday use case. That said, this is a 1st generation design, and I look forward to seeing what the 2nd generation has to offer when it has been finalised and put in to production.
More information on the DiffCase, and how to fit and use it can be found here.