I've been using TA App for sometime and it's incredible. It crossed on my mind that if we can download an app without leaving TA App, that would even be better! Therefore I do some research, Facebook & Flipboard is using this method as well, by using SKStoreProductViewController.
Doc link: http://developer.apple.com/library/i...roduction.html
Sadly this requires iOS 6, while if targetting ios 5 and below, the framework is usually weak-linked, this article might be useful: https://coderwall.com/p/ytschg