By using ZDO, you agree to the following (written from your point of view, of course):
Anonymous app usage data is collected about:
The data collected is used primarily for deciding what features need to be enhanced, and how to provide a better user experience for ZDO users.
The app isn't entirely free. It does come with In-app purchases for premium filters. However, ZDO was a side-project to teach myself a little about GPU Image processing on iOS, and also to learn a bit about In-app purchases and about building great User Interfaces.