Right now, I'm trying to strike a balance between making info available to devs and respecting user's privacy. The site gets the emails and IP addresses of people who get apps but doesn't reveal those to the dev.

The only "metric" that's available is the number of codes that have been used.

I've thought about making an opt-in so developers can contact users later. This way you could get people's permission to follow them up with questions on the app. How does that sound?