It's amazing what you think of the little details. Go on!
Unfortunately, there is a reason why this is not done in applications: the scary password dialog. When you try to restore the IAP, the system asks the user for the password for their iTunes Store.
Not really the best user interface when a large ugly password dialog appears as soon as the application opens. The user (if configured for security) is likely to reject the dialog.
On the other hand, users are used to click the "Restore purchases" button. It makes sense that a password is required to restore a purchase, and thus it will give it.
Just follow the standard, normal, boring restore button. Keep thinking about these little things though!
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