After a few days of checking to hear of any problems, have upgraded my MBPro to MacOS Sierra (10.12).
Smooth update via the App Store. No operational issues at all to this point. Some actually useful new features listed at OSX Daily:
7 of the Best macOS Sierra Features That You’ll Actually Use
So far I have only had time to update one production system (Macmini6,2) to 10.12 and one test system (Macmini5,2) to 10.12.1. Both have SSDs. No real problems. That matches my experience with the Sierra Developer Previews.
One strong recommendation is to NOT do any of that "Storage Optimization" stuff. Confusion and problems abound. Wait for a month or two before even considering any of it. Otherwise, it is easy to misplace or delete your data.