Unfortunately, replacement apps have a very different purpose on iOS than they do Android; unlike Android, iOS doesn’t allow its users to switch default apps. That means that no matter how hard you try, you just can’t make Sparrow open up every time you click an email address. Mail will be the app that opens – not Sparrow.
To me, this is iOS’s biggest problem. Locked-down ecosystems are no big deal, as long as you can pick which apps do certain tasks. As of right now, that’s impossible. Apple is the gardener in this walled garden, and it isn’t a friendly one, either.
If Apple would allow a bit of freedom once these replacement apps make it through the approval process, then I think iOS would be much more popular with hardcore smartphone users. It certainly wouldn’t knock Android out of its top spot for customization, but it would be a welcome feature, nonetheless.
At this point, though, I’ve fallen too far in love with Android for a move like this from iOS to make me consider switching back. But I’m not like everyone else, which then poses the following question: if Apple gave you a way to pick your default applications, would you go back to iOS? Let me know in the comments!