After swiping right for hours, I have found that this is sadly only available in the US.
What I really liked about Sparrow was the "hold to mark as read/unread", tap title to see all emails in convo, swipe up/down for next/prev, and the unified inbox. If it has all those, I would consider it.
I couldn't find it in the app store but I did find it by click ing on one of the apps made by Google, then scrolled at the bottom and clicked on > Developer info and it was down the list.
It might be because it's not yet available to all in the App Store yet.
It happens to me some times when I submit an update of an app to the App Store. I get the update a few moments after receiving the "Ready for Sale" status from iTunes Connect but then my partner only got the update in the App Store a few hours later.
What I really liked about Sparrow was the "hold to mark as read/unread", tap title to see all emails in convo, swipe up/down for next/prev, and the unified inbox. If it has all those, I would consider it.