ODK Collect v1.28 is now available and adds the "exactly match server" form update mode! Learn more in the documentation.
In the next Central release, App User QR codes will turn this on automatically. Additionally, we will soon link to documentation within the Collect settings interface to help users make decisions about configuration options.
We should have come back to you with this earlier, @tomsmyth, but after long discussions we decided to avoid the word "sync" because a normal dialog without details is more idiomatic for settings (a full screen dialog would require moving away from standard Android components) and because we hope to work towards 2-way synchronization before long. We would like to reserve the “sync” concept for that.