[flybirdx101]

I am not sure that this can be applied to any kind of app. You have to give user as much as possible until the product becomes valuable enough for him to buy, and that's when update option should be displayed. For example, in the case of an email app, time-limited trial can actually be a better option. User get's used to it, maybe he stores some additional information inside it or uses some specific features. Just limiting a number of emails would not let the user see the full potential of the app.