In our Apple Watch 9 review, we said it's not a noteworthy upgrade if you have a Series 7 or Series 8, but if this is your first Apple Watch or if you're upgrade from a much older model ...
The only problem with the Apple Watch’s unprecedented ubiquity is that ... This is different from the Series 7, Series 8, and Series 9, which give users a choice of a 41mm or 45mm case.