Are there download fees associated with Twixl Publisher ?

When creating 'standalone' applications, these apps are always downloaded through the App Store, and Apple provides the infrastructure and bandwidth (at no extra cost, independent of the number of downloads).

When creating 'kiosk' or ‘storefront apps’, only the app and its inital (default) content are distributed via the App Store. E.g. if you have a series of issues, all issues that are added after the initial download, can only be hosted outside of Apple’s App Store infrastructure. This implies additional hosting fees when using this model.

Twixl media uses Urban Airship for hosting the different issues. More details about the per download pricing for in-app purchases and the per subscriber pricing for subscriptions is available on the Urban Airship pricing page.