Google+ for iPhone has most of the features of the Android app, but it doesn't support instant uploads and lacks the advanced settings from the Android app.
The app has been criticized for the non-standard interface. "Google+ app uses left-right swiping to change views in your 'Stream'. I see three: Incoming, Circles, and Nearby. The idiomatic iOS design for this would be a tab controller at the bottom with three tabs, one for each view," says John Gruber.
Other users complain that they need an invitation to use Google+ and a surprising number of people say that the app doesn't work well in iOS 5, which is still in beta and can only be installed by developers, at least officially. This shows that many of the 18 million Google+ users are developers and tech enthusiasts.