I purchased a copy of OmniFocus for OS X, and I'm seeing how this is a pretty excellent organization app. However, I would also like a copy for iOS, only to have my jaw drop at how there are separate copies for the iPhone and the iPad, and each version costs $20. I don't know whether I want to purchase both versions like that, or use the iPhone version on the iPad and a future iPhone, so to any users, do you think it was money well spent?