I disagree. After having experience with OpenSUSE and Nemo, I must say that zypper dup handles system updates (and their dependency hells) much better than zypper up, which is better suited for regular updates. No wonder it is recommended by both OpenSUSE and Nemo Mobile.

I agree that version --dup (by the way, it is dup for a reason) should be used, but zypper dup saved me from having to restore my Jolla during the last two system updates, when updating through GUI failed and neither version --dup nor ssu worked.