One year ago, two app developers launched a paid upfront camera app in a world of freemium apps. With several 'pro' features, it exceeded their expectations. It's a great story on how to believe in what you are building and ship even if you aren't 100% ready.
For instance, one of the most important features of a camera app is to be able to take a photo with the volume buttons. Halide didn't have that feature at launch but succeeded anyway.
Halide: One Year Later by Ben Sandofsky