Will my manuscript, written on the Windows client, work in the iOs client? Any restriction, or can I go back & forth at will?
Really curious to see how you were able to create a usable Scrivener interface on a iPhone screen.
Yes you can, but do read the whole of the Tutorial on your iPhone and follow the instructions for setting up Dropbox properly before you start on any important project—best to start with a test project to learn your way around it before working on something important and valuable.
And don’t expect it to have all the facilities of the Windows version, and do expect differences from the Windows version in accessing its features.
Also, you need to update your Windows Scrivener to 1.9.5, so read all the Knowledge Base articles concerning compatibility and fonts.
If all that seems like too much trouble as you have no interest in using Scrivener for iOS for any real purpose, stay with what you have until Windows v. 3 comes out. Remember too, Scrivener for iOS will cost you somewhere around €20, which is a lot to pay if you’re unlikely to use it (I have a number of those … I wish I could delete them from my “Purchased” list, as seeing them hurts! 
)
All that said, Scrivener for iOS is a fantastic app and well worth every penny!
Mark