A simple mirror device makes street photography with the iPhone easier and a little creepier.
Street photography can be intimidating, even if you're just out trying to grab some shots with your iPhone. It's hard to be subtle when you have to hold your phone up in that unnatural way. The Hipoflex is plastic snap-on partial-case with mirrors embedded in it, allowing you to hold your phone at hip height, and snap off a few images.
An angled mirror places the scene in front of your lens, while it just looks like you're texting away or playing Angry Birds. Ideally, this makes you able to grab truly candid shots without alerting everyone around you to the fact you're taking a picture. It reminds me a little of this SLR spy lens which made news a few years ago.
While I can definitely see the use of this accessory, at the same time it strikes me as a little sleazy (a fact not helped by the YouTube promo the creators made.)
No technology is evil on its own, so just make sure that you don't do anything distasteful with it. You can grab the Hipoflex for $20 from their website.