When working on Mister Bacon, I realized that the app could be viewed in two different stores. You have the overall app store and then you have the App Store within iMessage itself.
If you install it from the main app store there is a chance that the user might not be able to find it after. More details on that in another post.
When using your iTunes link to the app store be sure to include &app=messages.
This will make it so that when the user clicks on the link via their mobile device, it will pop up in the iMessage App Store automatically.