When doing the manual merges, freebsd-update asks you to confirm the merges look correct after you've done all of them. If you answer 'n' to any one of the confirmation, freebsd-update exits entirely. This forces you to restart the entire process (including all of the manual merges). This is a significant regression compared to mergemaster. During a major-revision upgrade, this can be a very large amount of time wasted. Freebsd-update should prompt to confirm each merge after you've done just that merge. If you answer 'y', proceed to the next merge. If you answer 'n', redo the merge of just that file.
Wow this is old. I don't even know if it's relevant anymore. Feel free to close it.