We’re a MUS family. We’re using the old version, but that simply means we use the old teacher’s manuals/dvds. The workbooks offered now go with the new manual. That means they have an extra workbook page per lesson for the ‘common core’ concepts MUS had to add in to keep their accreditation. We skip that page for each lesson.
Also, the teacher’s manuals were updated to teach that new content and some explanations were streamlined/clarified from the original lessons. But the first 6 workbook pages for each lesson are still the same as before the revision, as are the tests.
Why did we stick with old manuals? Because we already had them! I’m not investing hundreds of dollars more for new manuals. Important to note that only the younger level manuals up to Zeta were updated. Not the older levels (Pre Algebra on up).