Possibly worth it for professionals; defintely not worth it for non-professionals
The program is very simple on the computer side, which could be useful if you have no technical skills but alot of money so that you can deal with things like image stabilization via controlling the environment. This makes sense for professional uses since digital image stabilization results in image quality deterioration, but not for casual use since its virtually impossible to deal with these issues in casual movie shooting. For non-professionals this tool is essentially worthless though because of the limited feature set, definitely not worth the $15.
I could potentially see it being worth $200 for certain professionals. But honestly if you’re a professional you probably have products like photoshop, premiere and after effects which could do the job much much better (with greater effort but much greater payoff).
The “production quality” of the app is very nice though, it looks like a lot of money was poured into making a full featured interface for a slender program. Tyra Banks and other celebrities are financial backers of the app and have given it much publicity adding to its “glamour” factor and boosting its app store rank and publicity.
League of Legends Top 20 about Cinemagraph Pro