Wow this app doesn't just overlay a moustache image but the moustache actually follows you around in realtime. Never seen this technology before. Awesome!
Apple Photo Booth does something similar (although I don't think with moustaches.) While trying to search for that, I found another iOS app that can do this with 250 facial features including a moustache (http://itunes.apple.com/us/app/ace-freakyface-cartoon-mask/i...)
Are you kidding me? The tracking on that app is abysmal. It has not one, but two banner ads, one on the top, one on the bottom. Furthermore the UI obscures much of the image. And you have to purchase the pack that includes the mustache. There are many apps that do what Instagram does, but there is only one Instagram for a reason.
As I mentioned, I just found it while doing some searching. I hadn't actually downloading the app (so no, I was not trying to 'kid' you.)
But you made some fair points about what makes your app better (assuming that it doesn't have these problems.) If one looks at the app store description for your app and the other app, though, it is hard to tell the difference (other than the lowest common denominator language in the description of the other app suggests it may be crappy and the opposite may suggest the quality of yours.)
Having a video of your app might be useful to show that you get those things right, although people who buy via the webstore might not see it.