I'm using the iOS version of 1Password 4 since the early betas and was always using Dropbox due to the lack of iCloud Support in 1Password 3 (for Mac).
Today I got the invite and promptly installed the beta app and set up iCloud (instead of Dropbox, and yes, I selected release container). Then I set up my iOS devices to sync via iCloud too.
I have a few suggestions:
For the record: I'm using 1Password 4 Beta on 10.9, 1Password 4 (stable, from the App Store) on iOS 7 on my iPhone (5) and on iOS 6 on my iPad (mini).